Influence of physiological maturity types on reproduction efficiency of beef cattle in resource-constrained environments

C. Stock (17009988)

Supervisor E. C. Webb

1Department of Animal and Wildlife Sciences, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa

Abstract

The purpose of this study is to determine the influence that the different physiological maturity types, early- and late maturing, have on the reproductive efficiency of beef cattle in resource-constrained environments in Southern Africa. The different constraining resources which are prevalent in Southern Africa are rainfall, temperature and humidity, soil pH, soil cation exchange capacity, soil organic carbon content, soil phosphorous concentration and grazing capacity. Some of these proved to have a larger influence on the reproductive efficiencies of the cows, however research specifically related to their influence on different physiological maturity types is limited. Contrasting studies showed that certain breeds of small and medium frame size, earlier maturing, had higher reproductive efficiencies in resource constrained environments while others showed that large frame size, later maturing, had better reproductive efficiencies. Age at first calving and inter-calving period were the two measurements of reproductive efficiency used.

Introduction

Agriculture worldwide faces many challenges in meeting the food demands of the ever-growing population. In order to keep up with the demand for food production, meat producers aim to produce animals most efficiently and economically, whilst meeting consumer preferences.

In South Africa, we face many challenges due to our climatic conditions which causes many resources to become constrained. Such constrained resources; grazing quality influences by rainfall and temperatures, soil pH (acidity), soil phosphorous (P) concentration, soil organic carbon content and soil cation exchange capacity; have negative or positive relationships with the reproductive efficiency of beef cattle. Farmers generally do not have enough funds to supplement poor grazing conditions, for example with licks, therefore using animals that are adapted to the specific bioregions are crucial to grow and reproduce at optimal efficiencies.

Certain physiological types and sizes are better adapted to a specific bioregion, allowing them to have increased productive and reproductive performances.

The more animals that a farmer can produce, the more food available and the more money he can make. Cattle that perform best in a certain area must, therefore, be used, which are generally those that are adapted and have the best reproductive performance.

Influence of frame size on production and reproductive efficiency

Frame size

The frame size of cattle plays a vital role in both the reproductive efficiencies of the cattle and their production in terms of weaning and slaughter weights. It is important to understand the relationship that adaptation plays, and its influence on the ability of the animal to grow and reproduce in the constrained environment. We therefore look carefully at the factors that influence this adaptation and one of these is cattle frame size.

Cattle frame size is generally categorized in 3 groups namely measured by the 18 months of age hip height, heifers are either small (>124cm), medium (125-135cm), or large (>136cm) (Taylor, 2006). Cows are studied further in terms of being of first, second or greater parity groups. In the study conducted by Taylor (2006), it was discovered that a small and medium frame size in heifers leads to a higher calving rates compared to cows with a large frame size. Considering that the aim is for higher calving rates, especially when beef breeds are concerned, the choice of a small to medium frame size is preferred. This is only one of the reproduction factors that is influenced by frame size. Calf survival rate was similar for heifers of all frame sizes in all of the parity groups.

Weaning rates of second parity cows with a large frame size (34.2 + 11.27) were lower than the weaning rates of medium (79.0 + 4.67) and small (82.9 + 5.58) frame sized animals. Birth weights of calves of large frame size cows were notably higher than those of medium and small frame sizes. Calves which were weaned by cows of first parity of a small frame size, had lower weaning weights than those which were weaned by cows of medium and large frame sizes, but large frame sizes tended to wean heavier calves when compared to medium and small frame size in the parity group of three or more. Calves of large frame size, first parity cows had a greater pre-weaning average daily gain compared to calves from small frame size, however, the calves from medium size, second parity cows outperformed those of large and small frame size, whereas calves born to third and larger parity cows of larger and medium frame had a higher pre-weaning ADG compared to small framed cows (Taylor, 2006).

Kilograms of calf production per cow bred is higher for medium and small frame size cows in comparison to large frame size. Medium and small frame females have larger calving and weaning rates and calved earlier, in addition per cow exposed there was more kilogram of calf produced compared to the large frame size females.

The growth performance of their calves to weaning and fertility, performance traits, of large frame size were generally comparable to those of smaller cows in the third and larger parity group. The reproductive efficiency of large frame sizes all parities were lower than the medium and small as a result of later calving dates. Considering the results obtained from this study, there is evidence that cattle of a small or small frame size offers the best reproductive efficiencies adapted in the harsh arid Southern African climate. Therefore, cattle in Southern Africa are selected for adaptation to the hot and arid climatic regions, farmed extensively with minimal supplementary feeding, It is recommended that the cow frame size which will be most efficient would be a medium frame (Taylor, 2006). Animals of medium frame have similar fertility levels to those of small frame size, however they had comparable or even superior performances in growth compared to large frame cows (Taylor, 2006).

The environmental resources accessible to a population of animals selected for adaptation to an environment, are optimally distributed amongst the productive and reproductive ability of the animal population as suggested in Beilharz et al., (1993).

However, in the study on Bonsmara cows by Visagie (2012) a positive relationship exists between reproductive efficiency and their mature weight (Visagie, 2012). This is an indication of a propensity for Bonsmara cows that are greater than the average size to have a higher reproductive efficiency compared to smaller cows. These results suggest that the available resources from the environment do not have a curbing effect on the reproductive efficiency of cows in SA which is unexplained and calls for further investigation and discussion (Visagie, 2012). This is most likely due to the breeding and selection of cows which are adapted to this particular environment and therefore perform optimally by having lower requirements of the limiting resources.

The growth curve and mature size

Additive gene action, genetic and non-genetic factors determine the individual’s growth and an interaction occurs with environmental influences (management, climate and nutrition), with intrinsic factors (age, sex and physiological status) as well as other extrinsic factors (Visagie, 2012). Growth occurs in a sigmoid curve which contains three phases starting with the self-accelerating phase, the linear phase and ending with the self-decelerating phase. The self-decelerating phase begins when the animal nears its mature size in which there is a limitation due to genetics on additional growth which is triggered by hormonal signals (Visagie, 2012).

Management, climate (temperature, rainfall) and nutrition influence the rate of the growth curve and mature size of the animal. The shape of the growth curve however remains the same and cannot be changed through selection.

Growth rate and maturity types

Growth rate and puberty

At the beginning of their original oestrus, heifers reach puberty after which a normal luteal phase occurs (Moran & Quirke, 1989). Size, breed, weight, plane of nutrition and social environment are factors which have an influence on the age at which puberty is reached in heifers (Moran & Quirke, 1989). Puberty and first ovulation are not the same thing as some heifers are unable to reproduce for quite some time subsequent to their first ovulation (Moran & Quirke, 1989). Despite aiming for a younger AFC which is suggested to increase the number of calves born to an individual, it is imperative that AFC is not reduced to before sexual maturity as incidences of dystocia are greater (Visagie, 2012).

Breeds which grow faster and reach a larger mature size, are of an older chronological age at puberty than breeds which weight gain at a slower rate and with a smaller maturity size (Martin et al., 1992). When breeds of large mature size are used as sires, the heifers tend to reach puberty later and heavier weights than heifers of smaller mature size sires (Martin et al., 1992). It is evident that puberty does not occur at a specific chronological, but rather a specific physiological age (Hafez & Hafez, 2008). This is due to the hormone interactions and the resulting interaction of these hormones on the target tissues which determines when puberty onset occurs (Visagie, 2012).

The relationship between age, live weight at puberty and growth rate as well as the effects of growth rate are difficult to distinguish (Lawrence & Fowler, 2002). Puberty is reached at a younger age in heifers with a higher growth rate (Visagie, 2012). Body composition differences occur between late- and early maturing breeds at comparable live weights which suggests that critical body protein or fat proportions can be the cause of puberty being induced (Lawrence & Fowler, 2002).

Growth rate and reproduction

Selection for increase growth rate has been widely done especially in beef cattle breeding. Because of this relationship between growth rate and reproduction has been studied yet still requires more research (Scholtz et al., 1990). Many studies have shown growth and reproduction traits to have unfavourable correlations, therefore the selection for increased growth rate can have negative effects on reproductive efficiency (Scholtz et al., 1990).

There are contrasting studies of cows which have high pre-weaning growth that have been shown to have raised more calves over their reproductive lifetime, with less calve mortalities and earlier calving (Burrow et al., 1991). Angus females in a study by Archer et al., (1998) showed that their reproductive performance, when a high growth rate is selected for, was similar when deliberate selection did not take place. In the same study it was discovered that Angus females which underwent selection for slower growth rates were showed to have significantly inferior reproductive performance compared to the others selected for higher growth rates and unselected individuals. This means that animals with a lower growth rate have lower fertility which is undesirable (Webb et al., 2012).

More research on this topic is required to make conclusive decisions on the extent to which growth selection has an effect on the efficiency of cow reproduction. If this can be done, selection for growth and fertility can be done simultaneously and without unfavourable effects.

Mature size

In the study on Bonsmara cows it was determined that mature weight has a positive relationship with their reproductive efficiency. According to theories by Beilharz et al. (1993), Fisher (1930) and Falconer & King (1953) it is suggested that increasing the population mean for cow size past an upper limit set by the availability of environmental resources will cause in a drop in the mean of the reproductive efficiency of the population (Visagie, 2012). In extensive South African conditions Taylor (2006) found that larger Santa Gertrudis cows are less efficient that smaller- and medium framed cows, however Visagie (2012) found the opposite in Bonsmara cows which suggest a positive relationship between their reproductive efficiency and mature weight (Visagie, 2012). Bonsmara cows that are of a larger than average frame size have higher reproductive efficiency when compared to smaller cows.

This implies that despite their higher nutrient requirements for maintenance, the cows of a larger frame size have higher reproductive efficiency because they are more efficient utilizers of nutrients. Another factor is that under conditions of limited environmental resources, larger framed cattle will have larger body reserves for utilisation in reproductive processes, resulting in a higher reproductive efficiency (Visagie, 2012).

Constrained resources and their influence on beef cow reproduction and efficiency

South Africa, in terms of agricultural production and beef production in particular, can be viewed as a resource constrained environment and large parts are less than ideal for beef production. The bulk of beef cattle in South Africa are therefore produced extensively where resources are constrained. This is supported by many characteristics such as poor grazing quality, especially due to seasonal variations, with certain areas yielding poor quality grazing. Farmers often do not have the resources, capacity or finances to supplement feeding according to the nutritional requirements of livestock. Due to these characteristics, the adaptability of the cattle is increasingly important in the efficient production of beef cattle in South Africa (Webb et al., 2012).

In order to understand the influence of physiological type of the cow in these environments, one must first consider the influence of these resources on reproductive factors within different bioregions (influenced by different climates and environmental factors). Constrained resources in SA are temperature and humidity, soil pH, rainfall, soil cation exchange capacity, grazing capacity, soil phosphorous (P) concentration and soil organic carbon content (Webb et al., 2017). ?

Temperature and humidity

Environmental temperatures directly influence animal production (Visagie, 2012). In South Africa a major concern is the influence of high summer temperatures on production systems (Bonsma, 1983). Just a slight increase in the core body temperature will have a great influence on the reproductive and productive abilities of cattle (Finch, 1986).

In Nguni cattle, which are a small to medium framed beef cattle breed and are very well adapted to bioregions which are typically resource constrained, higher temperatures have a negative effect on the inter-calving period (ICP), increasing the ICP when calving occurs during colder months such as autumn and winter as much as 30 days longer in winter compared to spring. In summer and spring calving cows, the ICP was between 399.8 ± 73.30 and 402.8 ± 101.76 (Mkhize et al., 2018).

In Bonsmara cattle, a breed which was bred to live and grow in the South African climate. A large frame side and late maturing breed which is well adapted to the unforgiving southern African bioregions and climates. The feed intake of animals is linked to the rate of digestion, which is influenced by many environmental factors, temperature being one of these factors. When cattle experience high ambient temperatures, humidity, air movement and solar radiation, they can fall victim to heat stress. When these factors combine and exceed the thermo-neutral zone’s upper limit, they reduce their feed intake and rumen retention time; this results in a reduction in nutrient intake resulting in a possible negative energy balance. This negative energy balance has an undesirable impact on the growth and size traits, as well as the reproductive traits. Temperature has a negative influence on reproductive traits, causing an increase in the age at first calving of cows and the inter-calving period, and a decrease in the reproduction index (Webb et al., 2017).

Figure 1 The maximum annual temperatures according to AGIS (2010) (Visagie, 2012)

Rainfall

Roughly 65% of the South African rangeland has an average annual rainfall of 600 mm or less and is therefore arid or semi-arid (Schulze, 1997). These areas have a high occurrence of seasonal or annual droughts, therefore rangeland is regularly the single source of feed and is seen as a resource for the extensive livestock industry (Snyman, 1998). Rainfall influences the veld type that occurs in the area, higher rainfall areas are predominantly populated by sour-veld, being of poorer quality and palatability. Low rainfall areas have good quality grazing, sweet veld and offer the animals grazing the veld with highly palatable and good quality grazing (Tainton, 1999). Rainfall influences animal production in both the short- and long-term, with the long term effects mainly on soil fertility and vegetation distribution (Visagie, 2012). The production and vegetation distribution is influenced by rainfall through its distribution, magnitude, concentration and variability.

For Nguni cattle in the Grassland and Savannah biomes, more rainfall occurs in spring and summer which can attribute to the yielding of more forage and subsequently better reproductive performances. A higher rainfall in the Grassland Biome occurred in autumn, than the Savannah Biome. Because of the temperatures being too low, quality re-growth was not promoted and therefore the higher rainfall would only marginally contribute to the quantity and quality of the forage (Mkhize et al., 2018). The studies have shown that due to them being well adapted to the South African climate, rainfall and season do not require much interference nutritionally from the environment.

For Bonsmara cows, a significant negative impact on all size, reproduction and growth traits was caused by rainfall. Higher rainfall resulted in an increase in the reproductive index, however the impact of rainfall is negative because of the large influence it had on the quality and quantity of forage (Webb et al., 2017).

Figure 2 The annual rainfall in South Africa according to AGIS (2010) (Visagie, 2012)

Soil phosphorous (P) concentration

Phosphorous is widely known to be deficient in forage produced on rangeland in South Africa (Visagie, 2012). Phosphorous deficiency is related to poor growth in young animals plus low weight gain in animals which are animals (Visagie, 2012). Low dietary P intake is also related to a decrease in milk production and poor fertility (McDonald et al., 2010). In studies at Armoedsvlakte in the North West province, severe P-deficiencies were found and is was observed that these P-deficiencies caused poor reproductive performance, as well as stunted growth, high mortality rates and reduced feed intake (De Waal et al., 1996; Read et al., 1986). Other studies showed no effect of different P levels in the reproductive and performance efficiencies of cows throughout southern Africa?(Visagie, 2012). It can be reasoned that P supplementation causes a variety of animal responses in a variety of environments and the response to improved P nutrition could therefore be to a number of reasons such as lack of energy or protein, not of P in their diet (Visagie, 2012).

In Bonsmara cows, soil P concentrations showed to have a significantly negative relationship with the reproductive traits. This implies that an increase in soil P results in a decrease in reproductive efficiency. This result caused confusion because it is common knowledge that P-deficiency is associated with suboptimal and abnormal fertility and growth. The supplementation of P has been shown to have a major positive impact on the growth, size and reproduction of beef cattle in South Africa (Webb et al., 2017). South Africa is known to have large areas which contain P deficiencies in the soil. Because of these known deficiencies, it would be expected that a positive relationship between production and soil P, reproduction traits would exist. Despite these findings, in South Africa P-supplementation is often given to cattle (Webb et al., 2017). It is also observed that because of these deficiencies, that P-supplementation would be effective in P-deficient areas, but in areas with adequate and marginal P-soil levels more P-supplementation may be required to resolve marginal deficiencies.

Figure 3 South African soil phosphorous status according to AGIS (2010) (Visagie, 2012)

Soil pH

It is a measure of the soil alkalinity or acidity (Visagie, 2012). Soil pH is a main factor that has an influence on plant species composition through soil properties (Visagie, 2012). Soil pH influences the soil’s biological, chemical and physical properties due to the pH of the soil influencing the formation and stabilisation of aggregate structures and the dispersion of clays, which majorly influences the movement of air and water (Visagie, 2012). Soil pH has an influence on the nutrient availability to soil microbes and plants (Brady & Weil, 2002). The increasing acidity of a soil is a naturally occurring process in soil formation and occurs when the production of H+ by the soil is faster than it consumes H+ (Visagie, 2012).

In Bonsmara cattle, soil pH had a significant, positive relationship with production efficiencies and the reproductive index. This suggests that a lower soil pH will have a negatively influence production traits. Soil pH is related to rainfall, in higher rainfall areas, lower soil pH is experienced which has a negative influence on cow production and reproduction traits. This is because rainfall directly influences feed quality (Webb et al., 2017).

?Figure 4 The natural soil pH in South Africa according to AGIS (2010) (Visagie, 2012)

Soil cation exchange capacity (CEC)

The definition of soil cation exchange capacity (CEC) is “the sum of total exchangeable cations that any soil can absorb” (Visagie, 2012). It is a chemical property of soil of importance which is used to assess soil environmental behaviour and fertility (Visagie, 2012). CEC increases as organic soil matter and pH increases (Visagie, 2012). The larger the CEC of a soil the better its ability to preserve nutrient cations in a potentially available form for microorganism and plant absorption (Whitehead, 2000). A higher CEC reduces the susceptibility of the soil to leaching (Whitehead, 2000).

In Bonsmara cattle, cation exchange capacity (CEC) had a substantial negative relationship with birth and weaning weights, but a positive relationship with mature cow weight which implies that calves receive partial buffering in utero and during lactation against low CEC which poses for an interesting study (Webb et al., 2017). There was evidence to show that soil with a high CEC has greater cation retention ability and is subsequently more fertile. However, due to there not being any significant effect on the growth traits of Bonsmara cows by CEC it suggests that there is efficient management and nutrient supplementation on Bonsmara farms.

Figure 5 South African Cation Exchange Capacity according to AGIS (2010) (Visagie, 2012)

Soil organic carbon content

A measure of the organic matter content of the soil is the soil organic carbon and total nitrogen and is the fundamental factor that influences the quality of the soil and provides much of the water holding capacity and CEC of soils (Visagie, 2012). The organic matter of the soil also influences the establishment and stabilization of aggregates in the soil (Brady & Weil, 2002). The availability of N, P and S as organic materials in soils is expired by microbial enzymes (Visagie, 2012). Drainage, vegetation type and climate establish the level of soil organic matter (Brady & Weil, 2002).

In Bonsmara cattle, the soil organic carbon content showed a significant negative relationship between soil organic carbon content and age at first calving, but showed significantly positive correlations with RI and ICP (Webb et al., 2017).

Figure 6 The natural soil organic carbon content in South African according to AGIS (2010) (Visagie, 2012)

Grazing capacity

All the above environmental factors influence the quantity and/or quality of the veld. These have a direct influence in the grazing capacity of the veld. It is important to focus on the indirect effects of rainfall on grazing capacity. “Grazing capacity is the productivity of the grazeable portion of a homogenous unit of vegetation expressed as the area of land required to maintain a single animal unit over an extended number of years without deterioration in the vegetation or soil” (Tainton, 1999). Grazing capacity is used to calculate the stocking rate of the rangeland and is critical in maintaining the quantity of the rangeland available to the animals which affects the intake and animal performance (Visagie, 2012).

In Bonsmara cattle, grazing capacity exhibited a negative correlation with growth parameters, agreeing with the correlations between Bonsmara growth parameters and rainfall. In bioregions with more rainfall, more grazing quantity with lower nutrient quality was exhibited, often experiencing nutrient deficiencies. There was a positive correlation between the environmental component of the 12-month weight and grazing capacity, which agrees with the observed effects for post-weaning shock in young Bonsmara heifers and soil pH, with succeeding responses of compensatory growth at roughly 12 months of age (Webb et al., 2017).The negative correlation between grazing capacity and reproductive traits in Bonsmara is due to the rainfall effects, species composition and, resultantly, veld condition.

The more animals that a farmer can produce, the more food available and the more money he can make. The best performing animals in a certain area must therefore be used, those that are adapted and will have the best reproductive performance.

Figure 6 South African grazing capacities according to the gc106 layer (2010) (Visagie, 2012)

Other environmental influences

Season of use

According to Tainton (1999), the terms “sweet”-, “mixed”- and “sourveld” refer to the “period of the year in which the natural grazing can sustain animal production without supplementation” (Tainton, 1999). This is an indicator of the production system type that is suited to the area (Visagie, 2012).

Biome (Grassland vs Savanah) a.k.a. Bioregion

Extensively farmed beef cattle in Southern Africa are subjected to a variety of relatively harsh climatic conditions such as low rainfall, high temperatures and a range of soil pHs. These characteristics affect reproductive efficiencies of cattle and because of poor grazing quality and seasonal changes. Because of the differences in nutritional value of the different biomes’ vegetation, ICP is significantly affected (Mkhize et al., 2018).

In research conducted by Visser (2012), results showed that the influence of individual breeders on reproductive index is 22% compared to the 5% influence of bioregion on RI.

Reproductive factors

The factors that are of importance when determining the efficiency of a beef herd are reproduction and calf survival rate (Visagie, 2012). Inter-calving period (ICP) and age at first calving (AFC) are the frequently used reproduction traits which are used to evaluate reproductive performance (Visagie, 2012).

Age at first calving (AFC)

AFC affects the cow size and the number and weight of calves produced, also the annual genetic progress for stud farmers, and is therefore an important reproduction trait for beef cattle produced (Visagie, 2012). AFC encompasses a number of different factors including puberty, the ability of the cow to have successful conception, gestation and delivery of a calf (Bormann & Wilson, 2010). Any environmental characteristic that influences one of the above-mentioned factors can have an influence on the AFC of a heifer (Visagie, 2012). AFC expression is also limited by the season in which the heifer is born, the season in which she is bred and the initial breeding season (Bormann & Wilson, 2010). In beef heifers, AFC occurs anywhere between two or three years of age, associations with dystocia sometimes occur with earlier mating of heifers and therefore requires good management (Visagie, 2012).

Inter-calving period (ICP)

The inter-calving period (ICP) is an important trait in determining the fertility of a cow and we aim to minimize the postpartum anoestrous period after calving in order to decrease the ICP. By decreasing the ICP the cow will produce more calves over her productive lifetime. Cows require ideal body conditioning as well as a certain weight in order to conceive. According to the study conducted by Visser in 2012, bioregion had very little effect on the ICP. The effect of breeders explained a 16% variation in the ICP caused by the environment (Webb et al., 2012). Cows which calve in spring and summer have shorter ICPs then those that calved in autumn (Mkhize et al., 2018).

Conclusion

The reproductive efficiency of beef cattle is influenced by a large number of intrinsic and extrinsic factors which make it particularly difficult to determine the exact reason for varying efficiencies. In South Africa, because of the harsh and arid climatic conditions, beef cattle which are produced extensively and with little or no supplementation must be adapted to the environment. Studies showed that in certain environments small and medium sized cattle outperformed large cattle, yet others showed the opposite. Because of these conflicting results, this subject requires more research trials pertaining to which maturity type performs the best in these resource constrained environments. There has been little research done on the effect of production region on the reproductive efficiency of beef cattle. Overall the type of cow used will influence the reproductive efficiency in a specific production region, the specific type for each region is where the research falls short which is largely due to the wide range of different production regions throughout the country.

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