Study of some factors effecting post-partum oestrus and fertility in two beef breeds.

Abstract

Animal Production in Australia Vol. 15 STUDY OF SOME FACTORS AFFECTING POST-PARTUM OESTRUS AND FERTILITY IN TWO BEEF BREEDS G.J. SAWYERa and M.J. CARRICK SUMMARY The interval from calving to first oestrus or conception was similar in Hereford and Wokalup multi-breed cows, and the first calving cows were later in both respects. The temporary removal of calves from adult cows caused a small reduction in calving to first oestrus interval in one year and no change in calving to conception interval in either year. In the higher milking Wokalup first calvers, the calf withdrawal caused an increase in both intervals in one year. INTRODUCTION For maximum profitability in a beef enterprise in South Western Australia all cows should calve every 12 months, within a compact period. The length of the post-partum anoestrous interval has been shown to be a limiting factor in achieving this aim in other environments (Dunn et al. 1969; Tervit et al. 1977) but there are few data available on the resumption of cyclic activity after calving, or the factors which affect it, under seasonal conditions in the South-West. This paper presents data on the return to cyclic activity and fertility, and the infuence of a calf withdrawal strategy in two widely differing cattle breeds. MATERIALS AND METHODS These studies used first calf and mature cows of the Hereford (H) and Wokalup (W) breeds. The 'Wokalups' are a composite of Charalois, Brahman, Friesian and Angus or Hereford, which are later maturing and have a high milking ability (Carrick and Robertson 1980). Cattle were set-stocked at 1.1 cows/ha in paddocks which held single sire mating groups of about 25. They grazed annual pastures consisting of sub-clover, rye grass and volunteer annual species. Supplementary hay and grain were fed each year as calving commenced (beginning of April), and continued for about 90 days. In experiment 1 (1979), 101 mature H and 81 mature W cows were divided among a control and two treatment groups to examine the effect of removing the suckling stimulus of the calf on the post-partum anoestrous interval. Control cows (40 H and 29 W) suckled their calves throughout, while the other two groups had their calves withdrawn for 48 hours at either 35 - 40 days or 50 55 days after the median calving date for their group. In addition, 20/39 first calf H and 15/35 first calf W cows had their calves withdrawn for 48 hours at 55 - 60 days after their median calving date. The remaining first calf cows acted as controls. In the second experiment (1980) which used 176 H cows and 223 W cows, calves were either withdrawn or left with their dams within each paddock group. Calf withdrawal commenced on day 35 post-partum and continued for 48 hours. In both experiments cyclical oestrous activity was detected by hormone-treated steers (Sawyer and Fulkerson, 1981) or the use of tail-paint verified by assay of serum progesterone collected each week. ab Dept. of Agriculture, Bunbury (a), Perth (b), Western Australia. 573 b Animal Production in Australia Vol. I5 Observations of marks left by chin-ball mating devices worn by the steers, and later the bulls during mating, were recorded three times every week. Pregnancy diagnosis was carried out 12 weeks after mating ceased and calving data were collected. Data were analysed using GENSTAT Multiple Regression routines, including the factors: calf withdrawal, cow age, breed and their interactions and paddocks within cow age x Breed (1979), or cow age, breed, calf withdrawal, and their interactions (1980). Fitted (least squares) means and standard errors were extracted for significant effects. Discontinuous distributions were analysed by chi-square methods. RESULTS (i) The interval from calving to first oestrus Over 90% of cows of both breeds had shown at least one oestrus by 80 days after calving in 1979. In 1980, the onset of seasonal pasture (especially clover) growth was relatively early, and a similar proportion had shown oestrus by 60 days after calving (Fig. 1). There was no significant effect of breed on the calving to first oestrus interval in either year, but in both years first calving cows returned to oestrus later than mature cows (Fig. 1, p < 0.01). In the first year calf withdrawal significantly lengthened the calving to first oestrus interval in first calving Wokalups (Table 1, p< 0.05), but in all other groups this interval was unchanged. In the second year the time to first oestrus was about 7 days shorter in cows from which calves were withdrawn (Table 1, p< 0.01). Figure 1 The percentage of cows having shown oestrus as a function of the number of days after calving. 574 Animal Production in Australia Vol. 1.5 Table 1 The significant main effects on the mean (2 S.E.) calving to first oestrus interval in Herefords and Wokalups in both experiments (ii) The interval from calving to conception and the level of fertility The distribution of calving to conception for all COWS showed that there was no significant effect of breed or age on the time when cows conceived. However, there was a significant year effect on this distribution (p< O.OOl), with cows in 1980 tending to conceive at the second or third oestrus after calving, probably due to the better season and earlier cycling activity. Despite the significant effect of calf withdrawal on the calving to first oestrus interval in the second year, it did not follow that cows conceived earlier. In the first year there was no significant effect of age or breed on the number of days from calving to conception, but Wokalup first calvers which had their calves removed conceived 27 days later (92.0 vs 65.0 days) than controls (p< 0.05). In both years first calving proportion of cows joined than did this difference significant (77% breed or calf withdrawal treatment year (average 89.5%). (iii) cows dropped less live calves as a mature cows, but only in the first year was vs 90%, p< 0.05). There was no effect of on the live calving percentage in either The calvinq to calving interval The calving to calving intervals measured in both years ranged from 349 + 4.9 days in mature Hcows to 382 + 6.9 days in W first calf cows. In both years there was no significant effect of calf withdrawal or breed on the calving to calving interval. Only in the Wokalups was there a significant effect of age on the calving to calving interval (382 days for first calvers vs 350 days for matures). DISCUSSION This study highlights the good fertility that can generally be achieved in cattle herds in South Western Australia when the nutritional requirements 575 Animal Production in Australia Vol. I.5 of breeding cattle are closely matched to the seasonal production of pasture. Reasonable pregnancy rates (85% and above) and calving to calving intervals of approximately 12 months were maintained in both breed types. The calving to first oestrus intervals were between 30 and 50 days shorter than reported from cattle run in the United States (Dunn et al., 1969) and New Zealand (Morris et al. 1978; Tervit et al. 1977). First calving cows dropped fewer live calves, returned to oestrus and conceived significantly later than mature cows of both breeds. This finding concurs with most published work (Tervit et al. 1977; Knight and Nicoll 1978) and is probably due to the extra demands of lactation imposed on young cows still growing after their first pregnancy. This is verified by the poorer performance of Wokalup first calvers, which produced about 30% more milk than Herefords. They were the only group to have a significantly longer calving to calving interval in 1979. Reduction of the calving to first oestrus interval by calf withdrawal in experiment 2 is similar to the trend observed by Smith et al. (1976), though not as dramatic. In fact, this result had little bearing on the final outcome - the proportion of animals producing live calves in the following year. In addition, the calving to conception interval was not affected by calf withdrawal treatment, and in these circumstances, the effort required for calf removal was not justified. In fact in one year the treatment significantly increased the calving to first oestrus interval in a small group of first calf w cows. This was probably due to the extra lactational stress on W first calf cows, and the small number of animals used. ACKNOWLEDGEMENTS Staff at Wokalup Research Station, especially M. Sumors, are thanked for management of the experimental cattle and P. Donnelly and J. Speijers assisted greatly with analysis of data. Funding was provided by the Australian Meat Research Committee. REFERENCES CARRICK, M.J. and ROBERTSON, D.E. (1980). 13:505. Proc. Aust. Soc. Anim. Prod. DUNN, T.G., INGALLS, J.E., ZIMMERMAN, D.R. and WILTBANK, J.N. (1969). J. Anim. Sci. 2:719. KNIGHT, T.W. and NICOLL, G.R. (1978). Proc. N.Z. Soc. Anim. Prod. 38:175. N.Z. J. Agric. Res. MORRIS, S.T., PLEASANTS, A.B. and BARTON, R.A. (1978). 2:577. SAWYER, G.J. and FULKERSON, W.J. (1981). Anim. Reprod. Sci. 2:259. J. Anim. Sci. $=:266. Proc. N.Z. Soc. Anim. SMITH, M.F., MARES, S. and WILTBANK, J.N. (1976). TERVIT, H.R., SMITH, J.F. and KALTENBACH, C.C. (1977). Prod. 37:109. -- 576