Prediction of conception rate in extensive beef herds in north-western Australia. 1. Seasonal mating and improved management

Abstract

Statistical models for conception rate were developed using data collected at a mid dry season (August-September) muster from a controlled-mated and supplemented herd of 900 Brahman cross cows at Mt Bundey from 1980-84. Average conception rates were 74% for maidens, 25% for first-lactation cows, 51 % for 4-10-year-old lactating cows, 54% for >10-year-old lactating cows and 96% for non-lactating cows. Although year effects dominated, they were partially explained by severity of the dry season and were consistent across levels of the other factors. Pregnant maiden heifers weighed 13 kg more than non-pregnant ones at the end of mating, after allowing for the weight of the fetus and gravid uterus. Conception rate of first-lactation cows was not affected by month of calving, adjusted mid dry season weight or condition score, possibly because of narrow ranges in these factors based on selection. For mature lactating cows the main effects on conception rate were month of calving (+11% for September to -16% for December or later), previous lactation (+6% for having reared a calf), adjusted mid dry season weight (-16% for <300 kg to +9% for >350 kg) and condition score (-17% for backward and store to +16% for good condition). Corresponding effects for aged lactating cows were +14% for September to -19% for December or later calving, +8% for previously rearing a calf, and -24% for backward store and store to +23% for good condition cows. The high conception rates for non-lactating cows corresponded with high liveweights and condition scores. A low cost, practical implementation of these models is based on previous lactation status and condition score in the mid dry season, with pregnancy diagnosis added at the next stage. Reproductive classes could be segregated on this basis for improved management and nutrition and to gain an economic return on capital invested in cattle control.

Nutrient Requirements of Domesticated Ruminants

“…However, Morley et al (1976), from an analysis of results for groups of mature Angus cows grazing at different stocking rates, found an increase in the probability of pregnancy with mean weight at joining that amounted to 0.14 per unit of CS. Responses to CS are even more marked in extensive beef herds in north-western Australia (O'Rourke et al 1991). Graham and Clarke (1984) showed that CS is a good indicator of fat depth on live cattle, and therefore a useful aid in sales-by-description of animals for slaughter.…”

Breeding, Management and Environmental Issues at Peri-Urban Dairy Farms

“…Osoro and Wright (1992) and De Rouen et al (1994), concluded that BCS at calving significantly affected postpartum reproductive performance in cows. O'Rourke et al (1991) reported that cows with BCS of ≥8 had a conception rate 33% higher than those with score ≤5 (scale 3-9). Buffaloes in poor BCS had inactive ovaries and long postpartum anoestrus periods (Jainudeen and Wahab, 1987).…”