Calving dates and subsequent intercalving intervals in New Zealand beef herds

Abstract

The calving dates of spring-calving cows in New Zealand Angus and Hereford herds, taken from 350 and 240 herd-years respectively, and the intercalving intervals (CI) of cows in 95 Angus and 73 Hereford herds have been summarized. The relationships of each CI with the calving date which initiated it were also analysed. Results for each breed were analysed taking account of district, herd, year and cow age (in years), a total of 35 890 Angus and 22 397 Hereford records being used. The first-calving date (FCD) was identified for each herd-year, and 0-82 of Angus and 0-75 of Hereford cows were recorded as calving within 60 days of the FCD. On a herd basis, proportionately only 0-27 of Angus and 015 of Hereford herds had calving spreads of 80 days or less (defined as the time from the FCD to the last calving date). With barren years ignored, the CIs of cows averaged 370 days (Angus) and 368 days (Hereford). Two-year-old cows had on average a CI of 12 (Angus) or 7 days (Hereford) longer in 1974-75 than older cows, and the differences were both 12 days in 1975-76. Regression analyses showed that, on average, the later the calving date within a herd-year and age group, the shorter the subsequent CI. For cows calving early in the first year, the CI increased by 7 days for Angus and 5-4 days for Herefords for each 10 days before the mean calving date for the breed. There were significant effects of district and cow age on the regression estimates. The overall regressions were not consistent with those derived from British beef industry data.

Influence of weaning age on the reproductive efficiency of primiparous cows

“…Cows calving for the first time at 22/24 months of age were biologically more efficient than those that calved at older ages (Morris, 1984). Herds with a higher number of breeding heifers have a higher number of young cows, with lower average body weight, increasing the biological efficiency, provided the same reproductive rates are maintained (Beretta et al, 2001 Table 7 -Calf weight adjusted to 100 days of age and production efficiency averages at calving and weaning of 22-to 24-month-old primiparous cows weaned at different ages…”

Manejo de novilhas prenhes aos 13/15 meses de idade em sistemas a pasto

“…De acordo com Morris (1984), primíparas parindo aos 24 meses de idade são aproximadamente 9% mais eficientes biologicamente que aquelas que parem um ano mais tarde. Nuñez-Dominguez et al (1991) concluíram que não é econô-mico manter no rebanho fêmeas que passam um ano sem produzir ou parem somente aos 3 anos de idade.…”

Effects of early versus late spring calving on beef cow-calf productivity

“…The general distributions of calving patterns were similar in both early and late groups, but a lower percentage of calves was born in the first 21 d of the season in the early group than in the late group (51.5 vs. 61.8%, respectively). Morris (1984) studying calving distributions in Angus and Hereford cows in New Zealand found that early calving cows were delayed in achieving a successful subsequent conception.…”