BEEF BREED IN THE ARID SUB-TROPICAL ENVIRONMENT OF SOUTHERN AFRICA 

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CHAPTER 3 INTERRELATIONSHIP AMONG LIFETIME COW FERTILITY, COW SIZE, PRE-WEANING AND POST-WEANING CALF GROWTH IN SANTA GERTRUDIS CATTLE

(Article published in the Asian – Aus. J. Anim. Sci. 13: 353 – 355, July 2000, References updated to 2006)

 ABSTRACT

The study was conducted to determine the associations between lifetime cow fertility and cow frame size, also between lifetime cow fertility and pre-weaning as well as post-weaning calf growth in tropically adapted Santa Gertrudis cattle. A total of 2 506 Santa Gertrudis cows were divided according to their average lifetime calving interval (CI) into short calving interval (SCI, < 400 days, n = 914 cows) and long calving interval (LCI, > 400 days, n = 1 592 cows) groups. Calves were weighed at weaning at approximately 7 months of age. Hip height of cows and pre-weaning gain of calves of the SCI cows (135 cm and 1.01 kg/day) were significantly (p < 0.05) lower than those of the LCI cows (141 cm and 1.25 kg/day). Calves from SCI cows were born significantly earlier in the calving season than calves from LCI cows as measured by age at weaning (221 vs 189 days). As a result of compensatory growth there was no significant difference for yearling weight between progeny of SCI and LCI cows (348 vs 349 kg). It is concluded that SCI cows are smaller in size, with significantly lighter calves at weaning. A negative correlation exists between fertility and pre-weaning calf growth. Post-weaning calf growth is compatible with high cow fertility.
Keywords: cow frame size, calving interval, pre-weaning growth, post-weaning growth, Santa Gertrudis.

INTRODUCTION

Improvement of fertility and growth through selection in beef cattle are becoming increasingly important, as beef production is determined by the reproductive rate, growth rate of calves and weight of culled cows. It is generally accepted that smaller cows are more fertile under extensive grazing conditions because small body size is an adaptive attribute, but that larger cows produce more milk and, therefore wean heavier calves (Olson, 1994 Mercadante et al., 2000, Minick et al., 2001). However, success of the real practice in different breeds and under different production systems needs to be demonstrated and the effect of lifetime cow fertility on traits such as mature size, weaning weight and post-weaning growth rate need to be evaluated. Calving interval (CI) was used as a measure of reproductive efficiency in this study. The objective of this paper was to study the associations between lifetime cow fertility and cow frame size, and between lifetime cow fertility and pre-weaning as well as post-weaning calf growth in tropically adapted Santa Gertrudis cattle.

MATERIAL AND METHODS

Data was obtained from the Santa Gertrudis Cattle Breeders Society of South Africa. Calving and growth records were analysed from three production systems in the southern African Region over a 12-year period. These production systems were managed extensively and the animals had to survive on natural pastures with a summer and winter lick. The breeding seasons were limited to 90 days for heifers and 60 days for the cows. The calves were weaned between 7 and 8 months of age. The bulls were all fertility tested before the breeding season commenced and they were put in with the cows at a 4% ratio. Only cows, which had calved twice, or more were used in this study. Cows were divided into 2 groups according to their average lifetime CI: Those with a CI < 400 days (SCI); and, those cows with a CI > 400 days (LCI). Calving date, weaning weight, 12 month and 18-month weights were recorded. Hip height was also recorded as a measure of cow frame size. Data were analysed using the General Linear Models procedure of Statistical Analysis Systems (SAS 1995). Traits were analysed by the least squares means of variance and the model of analysis included affect due to CI (SCI and LCI), age of dam, previous lactation status, sex of calf, weaning weight, 12 month weight, 18 month weight, hip height of the cows and a regression effect of day of birth.

RESULTS

The least squares mean for weaning-, 12 month- and 18 month weight of calves, as well as hip height of the cows, for the SCI and LCI groups are presented in Table 2.1.
Cows with higher lifetime fertility (SCI) were significantly smaller and also weaned significantly lighter calves. These cows dropped 78% of their calves during the first half of the calving season, while only 52% of the LCI cows dropped their calves during the same period, resulting in calves of the SCI group being significantly older (221 days compared to 189 days) at weaning.
Post-weaning growth rate for the progeny from the SCI group of cows was significantly (p < 0.05) greater than those progeny from the LCI group, resulting in the actual weight for the two groups not differing significantly (p < 0.05) at 12 months of age. Additional compensating growth was evident in the progeny of the SCI cows resulting in significantly (p < 0.05) higher 18 month weights in favour of the SCI group.

DISCUSSION

Since the SCI cows were significantly smaller in size than the LCI group, it is likely that early and regular reproduction restrict mature size. Under extensive conditions, small size is a desirable adaptive attribute, generally associated with early and regular reproduction. This may be ascribed to high inherent fertility of the tropically adapted, synthetic Santa Gertrudis breed, which offers more flexibility under stressful conditions to increase productivity, without sacrificing expressed fertility (Swanepoel and Lubout 1992, Taylor and Swanepoel, 1999).
Seifert and Rudder (1975), Lalman et al. (2000) and MacNeil (2005), stated that cows with less than average live weight, tended to have lighter progeny at weaning due to reduced milk production. Reduced lactational performance may be partly responsible for the higher fertility of the smaller cows. The present study suggests that there may be a close relationship between cow fertility and progeny growth from birth to weaning age. LCI cows produced calves with the highest pre-weaning growth and the heaviest weaning weight. The least fertile cows were generally the heaviest (McMorris and Wilton 1986, Nesamvuni, 1995, Heuer et al., 1999) and larger (Olson, 1994, Haile-Mariam et al., 2004, Chase et al., 2005), with better udders (Taylor, 1995), with which they produced more milk (Van Raden et al., 2004, Windig et al., 2006). They were mostly those that missed at least one calving season. Perhaps they were able to recover more rapidly from the stress of reproduction and nursing a calf and build up better body reserves for a subsequent calving.
Reduced lactational performance as such has been suggested as a contributing factor to the improved fertility in cattle (Hetzel et al., 1989, Davis et al., 1992, Borman et al., 2004). If this is the case, it can be explained by the physiological interaction between lactation and depression of ovarian function that is related to pituitary dysfunction, which is associated with lactation (Short et al., 1994, Opsomer et al., 2000, Hooijer et al., 2001). During intense lactation, prolactin function is maximal, limiting the secretion of FSH and LH releasing factor. The duration of anoestrus is closely related to length and intensity of lactation (Hafez, 1980, Lopez-Gatius et al., 2001). Bulls were usually put with the cows two months after calving and milk production usually peaked at this stage. An attempt could be made to substantiate this by the fact that larger cows usually produce more milk (Seifert and Rudder, 1975, Bourdon and Brinks, 1983, Doren et al., 1986), therefore they calved later in the season. These results do suggest a negative endo-environmental interaction between fertility and pre-weaning growth. Other authors (McMorris and Wilton, 1986, Swanepoel et al., 1992, Savagea et al., 2004) agree that positive correlations between cow weight and either milk production or calf weaning weight exist. Bourdon and Brinks (1983) and Doren et al. (1986) reported a positive influence of weaning weight on cow fertility. Small cow frame size, reduced milk production and correspondingly lighter weaning weights are actually adaptive characteristics found in tropically adapted beef cattle (Rege, 1993, Tomo et al., 2000).
Davis et al. (1992) found compensatory growth in both the wet and dry seasons for a SCI and LCI group, with the largest proportionate difference between the two fertility groups being in the dry season. This suggests that there may have been a correlated improvement in efficiency when feed was limited. This possibility is supported by this study, as the main compensatory growth occurred between weaning and 12 months of age, corresponding with the dry (winter) season. Compensatory growth still continued to take place in the wet season (12 – 18 months), but the difference between the growth-rate of the progeny from the two CI groups in the wet period was not as big as between the weaning and 12 month period.
Calves from the SCI group may have been better adapted to grazing at weaning due to the likely lower milk production of the cows as indicated by the lower weaning weight of the progeny. These calves were therefore better adapted to the available grazing and could express the compensatory growth after weaning. The calves from more fertile groups may have had better developed rumens, as they were older and may have had to survive on less milk and more of the natural grazing than the progeny from the less fertile group. However, no work has been done to substantiate this and it should be investigated further.
Tomo et al. (1999) and Corbet et al. (2006) have maintained that there is no genetic antagonism between high cow fertility and post-weaning growth of their progeny, provided that strict selection is practiced for both traits. Selecting for growth rate alone may lead to reduced fertility (Olson, 1994, Archer et al., 1998). Meyer et al. (1991) reported a favourable genetic correlation between reproduction and growth traits in cattle, and Wolfe et al. (1990) also concluded that selection for weaning weight, final weight and muscling score had no detrimental effects on age at puberty in heifers. MacNeil (1988) also reported that male progeny with a relatively high growth rate were produced by cows which tended to be more fertile. This was also supported by Moyo et al. (1996).
Hetzel and Mackinnon (1989) concluded that high lifetime cow fertility measured in terms of the estimated breeding value for pregnancy rate, was not incompatible with the post-weaning growth rates of their progeny. Compensatory growth took place in the progeny of the high fertility group to such an extent that at 12 months of age there was no significant difference in the weights of the progeny between the high and low line fertility groups.

CONCLUSIONS

Cows of higher lifetime fertility (SCI) are smaller in size, have significantly lighter calves at weaning. Early and regular reproduction may restrict mature size. A negative endo-environmental correlation exists between fertility and pre-weaning calf growth.
Compensatory growth occurs after weaning especially in progeny from more fertile cows. The high post-weaning growth rates of the progeny of higher fertile cows therefore minimise the weight advantage of the calves from the less fertile cows even though the latter weaned calves with higher weights. The result is that at 12 months of age there is no significant difference in weight  between  the  two  groups.Post-weaning  growth  rate  is  therefore compatible with high cow fertility.

SUMMARY 
PREFACE 
ACKNOWLEDGEMENTS 
LIST OF ABBREVIATIONS 
LIST OF FIGURES 
LIST OF TABLES 
SECTION A 
CHAPTER 1 
1.1 GENERAL INTRODUCTION
1.2 REFERENCES
CHAPTER 2  NON-GENETIC INFLUENCES ON PRE- AND POST-WEANING GROWTH TRAITS OF A TROPICALLY ADAPTED BEEF BREED IN THE ARID SUB-TROPICAL ENVIRONMENT OF SOUTHERN AFRICA 
2.1 ABSTRACT
2.2 INTRODUCTION
2.3 MATERIAL AND METHODS
2.4 RESULTS AND DISCUSSION
2.5 CONCLUSIONS
2.6 REFERENCES
CHAPTER 3  INTERRELATIONSHIP AMONG LIFETIME COW FERTILITY, COW SIZE, PREWEANING AND POST-WEANING CALF GROWTH IN SANTA GERTRUDIS CATTLE 
3.1 ABSTRACT
3.2 INTRODUCTION
3.3 MATERIAL AND METHODS
3.4 RESULTS
3.5 DISCUSSION
3.6 CONCLUSIONS
3.7 REFERENCES.
CHAPTER 4  ,EFFECT OF HEIFER FRAME SIZE ON THEIR SUBSEQUENT REPRODUCTIVE PERFORMANCE AND ON THE PRE-WEANING PERFORMANCE OF THEIR CALVES 
4.1 ABSTRACT
4.2 INTRODUCTION
4.3 MATERIAL AND METHODS
4.4 RESULTS AND DISCUSSION
4.5 CONCLUSION
4.6 REFERENCES
SECTION B 
CHAPTER 5 TICK BURDENS OF TROPICALLY ADAPTED BEEF CATTLE AS INFLUENCED
BY SELECTED PHYSICAL AND PRODUCTION TRAITS 
5.1 ABSTRACT
5.2 INTRODUCTION
5.3 MATERIAL AND METHODS
5.4 RESULTS AND DISCUSSION
5.5 CONCLUSION
5.6 REFERENCES
SECTION C 
CHAPTER 6 
6.1 INTRODUCTION
6.2 REFERENCES
CHAPTER 7  RELATIONSHIP BETWEEN GROWTH PARAMETERS, SCROTAL CIRCUMFERENCE AND SHEATH AREA IN TROPICALLY ADAPTED BEEF BULLS 
7.1 ABSTRACT
7.2 INTRODUCTION
7.3 MATERIAL AND METHODS
7.4 RESULTS AND DISCUSSION
7.5 GROWTH PARAMETERS AND SHEATH AREA
7.6 CONCLUSION
7.7 REFERENCES
CHAPTER 8 ASSOCIATIONS AMONG GROWTH AND QUANTITATIVE TESTICULAR TRAITS OF TROPICALLY ADAPTED YEARLING BULLS FED DIFFERENT DIETARY ENERGY LEVELS. 
8.1 ABSTRACT
8.2 INTRODUCTION
8.3 MATERIALS AND METHODS
8.4 RESULTS AND DISCUSSION
8.5 CONCLUSION
8.6 REFERENCES
CHAPTER 9  RELATIONSHIP BETWEEN SCROTAL CIRCUMFERENCE, QUANTITATIVE TESTICULAR TRAITS AND GROWTH PERFORMANCE IN TROPICALLY ADAPTED YEARLING BEEF BULLS DIFFERING IN AGE 
9.1 ABSTRACT
9.2 INTRODUCTION
9.3 MATERIALS AND METHODS
9.4 RESULTS AND DISCUSSION
9.5 CORRELATIONS
9.6 CONCLUSION
9.7 REFERENCES
CHAPTER 10  IMPLICATIONS AND GENERAL RECOMMENDATIONS FACTORS AFFECTING THE PRODUCTION AND REPRODUCTION PERFORMANCE OF TROPICALLY ADAPTED BEEF CATTLE IN SOUTHERN AFRICA
SUMMARY
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