Effect of reproductive status, body condition and age of Bos indicus cross cows early in a drought on survival and subsequent reproductive performance

摘要

A herd of 802 Brahman cross cows, managed under extensive conditions (7000 ha paddock with twice-yearly handling) in a dry tropical environment, was studied during the severe drought of 1982-83. Twenty-one per cent of the cows died. Cows more advanced in pregnancy and those in poorer condition in the early stages of the drought had lower (P<0.05) survival probabilities. Cows aged over 7 years also generally had a reduced (P<0.05) probability of survival. Calf loss between confirmed pregnancy early in the drought and weaning after the following wet season was 31%. Calf loss from surviving cows was not higher than is usual in non-drought years. All deaths of lactating cows were associated with calf deaths. The practical use of these results in cost-efficient management for survival of cows in drought was then evaluated in a second study in which 293 cows were drafted into high- and low-supplement-requirement (HSR and LSR) groups in the early stages of the 1987 drought. Survival feeding in the HSR group commenced about 6 weeks earlier than would have been necessary in the LSR group. In both studies, reproductive status in the early drought period was a significant determinant of both body condition and conception rates early in the following year. Cows more advanced in pregnancy early in the drought were in poorer condition after the following wet season (P<0.05), but remained further advanced in pregnancy (P<0.05). Both body condition in the early part of the drought and age had minimal effects on performance in the following wet season, although younger cows tended to be lighter and have the lowest conception rates. Cows in better condition after the wet season had higher (P<0.05) pregnancy rates.