Factors affecting pregnancy rate in Holstein-Friesian cattle mated during summer in a tropical upland environment [Atherton Tableland, Queensland]
1993
Orr, W.N. | Cowan, R.T. | Davison, T.M. (Queensland Dept. of Primary Industries, Ipswich (Australia). Mutdapilly Research Station)
Data were collected at Kairi Research Station in north Queensland over a 12-year-period (1977 to 1988) for cows grazing fertilised grass pastures and receiving either no supplement or about 3.5 kg molasses per cow per day. There was considerable variation among years in the pregnancy rate after 3 inseminations, with a low of 39 percent and a high of 94 percent pregnancy. This variation from year to year was reduced for cows grazing pastures receiving 300 kg N per ha per yr after molasses feeding commenced in 1984-85. Much of the year to year variation in pregnancy rate was related to rainfall during the mating period. There was a positive association between pregnancy rate and rainfall up to 1000 mm, and this was associated with differences in growth of pasture. Much of the variation in pregnancy rate during summer may have been related to heat stress and the level of feed supply in the form of pasture and supplements
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