Winter lambing of aged Perendale ewes on Northland farms

Abstract

Abstract Aged Perendale ewes comprising 15–20% of a flock were induced to mate late in their non-breeding season and to lamb in June—July. The experiment was repeated for two years on several farms near Ngataki (34.5°S) and Kaikohe (35.3 °S) in Northland. Rams were joined on the same day to independent groups of progesterone-primed ewes; or unprimed ewes run with or without progesterone-treated ewes. Progesterone-primed ewes mated 2 days after rams were joined in late January–early February and 53 — 73% conceived to their first oestrous cycle and subsequently lambed over a 7-day period. A total of 79-95% of ewes lambed from their first two oestrous cycles after priming. Priming ewes in late December did not induce early mating. There was more variability in conception rate over 2 oestrous cycles without progesterone priming and almost no ewes lambed from their first cycle. However, between 43 and 83% of unprimed ewes lambed to their second cycle and most of the remainder to their third cycle. More unprimed ewes lambed to their second cycle when they were run with an equal number of primed ewes. High ram: ewe ratios (8–23 rams: 100 ewes) were used. Most rams were mixed-age Perendales, but some farmers used young 2-tooth rams and these did not induce early mating. Average docking percentage (lambs docked/ewes at docking) of early-lambed, aged ewes ranged from 96 to 106%, compared with 120% for mixed-age ewes lambing in spring. Winter-born lambs were weaned in late September and c. 1/3 were drafted directly to the works at 11.6–11.9 kg carcass weight. Virtually all lambs were drafted by mid November, providing an early start to the killing season. When winter-born lambs were grown through spring on one farm, first draft carcass weight averaged 15.8 kg in mid November. The cull ewes were killed in October–early November and, in the 1984–85 season, they produced only 2% ultralight (MM grade) but 22% overfat (MH + MF grade) carcasses compared with 29% ultralight and 8% overfat for spring-lambing ewes killed in autumn.