The relationships between liveweight, growth from weaning to mating and conception rate of Bos indicus cross heifers in the dry tropics of north Queensland

Abstract

Factors influencing the conception rates of 1332 Bos indicus cross maiden heifers in the dry tropics of North Queensland were studied between 1973 and 1986. The heifers, which were 112 and 314 Bos indicus (Brahman or Sahiwal) crosses with Bos taurus, were mated at 24-27 months of age over a 3-month period commencing in mid to late January. The effects of liveweights and growth rates on conception rate were initially assessed in separate models which always included cohort (year of branding group) as an additional factor. Cohort and liveweight at weaning, 18 months of age or the start of mating significantly (P<0.05) affected conception rate in maiden heifers. Response to liveweight was curvilinear, being marked for liveweights up to 125-150 kg at weaning, 200-225 kg at 18 months of age and 225-250 kg at the start of mating, with reduced response for greater liveweights. Liveweights of about 270 kg were indicated as targets at the start of mating in a typical year to achieve an 80% conception rate. Average daily gains during the post-weaning dry season and the dry season prior to mating did not influence conception rates after adjusting for cohort. Further analyses using models incorporating both liveweight and growth rate with and without the cohort effect gave indications that the significant cohort effect on conception rate was partly related to post-weaning dry season growth rate. F2 et seq. maiden heifers with low liveweights at either 18 months of age or mating had appreciably higher conception rates if they had gained weight in the post-weaning dry season, rather than losing weight.

Growth and reproductive performance responses to post-weaning supplementation of early and normally-weaned Brahman crossbred heifers raised in tropical rangelands

“…Overall, the parameter that explained the greatest variation for occurrence of pregnancy was PM.LW, which was, in general, greater for the NW compared with EW heifers. This is consistent with previous studies which have found that the most important factor affecting pregnancy rates of maiden heifers is PM.LW [ 35 , 36 ]. This outlines the long-term consequence of first dry season supplementation and WW on pregnancy percentage, a practical objective of this experiment.…”

“…The authors proposed a target LW (curfew) of 253 kg measured in October/November would result in an 80% of pregnancy for two-year-old heifers. Similarly, working with two-year-old Brahman cross heifers Doogan et al [ 36 ] et al proposed approximately 270 kg as a target LW at the start of mating (January) in order to achieve a 80% confirmed pregnancy at the end of a 100-day mating period…”

Sequential changes in ovarian follicular dynamics in Bos indicus heifers before and after nutritional anoestrus

“…Body mass and body condition therefore undergo oscillating patterns of increase during the wet season and decrease during the dry season (Holroyd et al, 1979). The severity of weight loss and decrease in condition have major effects on reproductive performance, with degree of weight loss during the preceding dry season and condition at mating correlating with conception rates in both heifers and mature cows (Doogan et al, 1991; O'Rourke et al, 1991).…”

Strategies for Increasing Beef Cattle Production under Dryland Farming Systems

“…There are in turn a range of factors associated with age of puberty including live weight, body condition score and breed (e.g. Doogan et al 1991); b) Post partum anoestrus interval, the time between calving date and when the cow recommences cycling, influenced by live weight, body condition score and breed, as well as lactation status; c) Time of conception after calving (e.g.…”