Management of highly fecund ewe types and their lambs for 8-monthly lambing. 1. Effect of lamb weaning age on ewe reproductive activity in spring

Abstract

The spring reproductive activity of ewes following a late winter lambing, and varying duration of suckling or lamb weaning age of 6-13 weeks, was investigated in 321 Booroola Merino x Dorset (BD) and 543 Trangie Fertility Merino x Dorset (TD) ewe records over 2 years and 238 Border Leicester x Merino (BLM) ewes in the second year. The ewes were joined about 12 weeks post-partum in November for 6 weeks, following lambing in July-August to conform to an %-monthly lambing regime. In the first year, ewes were run with vasectomised rams and oestrus, ovulation rate, and interval to first observed oestrus were determined under a simulated joining regime. In the second year entire rams were joined in spring following July-August lambing and oestrus, pregnancy, fetal number, lambs born per ewe joined and lambing interval were analysed. Amongst ewes rearing lambs, longer suckling significantly increased the interval to first oestrus and the lambing interval (P<0.01), but had no effect on the percentage of ewes expressing oestrus, percentage of pregnant ewes or lambs born. Significantly fewer ewes that lambed but failed to rear any lambs (LL), than ewes rearing lambs expressed oestrus, ovulated and became pregnant. This resulted in considerably lower lambing rates for LL ewes (95.8 v 137.2% lambs born, P<0.01). Reproductive activity was not greatly affected by ewe liveweight or liveweight gain during joining. BD and TD ewes had hgher pregnancy and lambing rates and a shorter lambing interval than BLM ewes. Ovulation rate and fetal number increased with the number of lambs being reared (0.20 � 0.08 and 0.11 � 0.04 per lamb, P<0.05). The results show that high pregnancy and lambing rates can be achieved from natural joining in the spring following late winter lambings within an 8-monthly lambing regime, when lambs are weaned prior to joining.

Effect of weaning pre‐ or post‐mating on performance of spring‐mated ewes and their lambs in New Zealand

“…While mating lactating ewes has been shown to prolong postpartum intervals in some studies (Mallampati et al 1954;Pope et al 1989), in others (Cognie et al 1975;Pope et al 1989;Fogarty et al 1992), it has been reported to increase pregnancy rates, ovulation rates, or litter size. The current trial showed breeding suckling ewes did not enhance or adversely affect ovarian CL counts, oestrus activity, pregnancy rates or litter size in ewes bred 68-73 days postpartum.…”

Idade à desmama e manejo alimentar na produção de cordeiros superprecoces

“…Wallace et al (1989), trabalhando com ovelhas induzidas, concluíram que as gonadotrofinas não foram fatores limitantes à prenhez de ovelhas lactantes até 42 dias após o parto. Fogarty et al (1992) postularam que não há interferência da intensidade da mamada na atividade éstrica de ovelhas e que o fotoperíodo é o principal responsável pela sasonalidade reprodutiva dos ovinos (Chemineau et al, 1992;Mandiki et al, 1990). No entanto, Mitchell et al (1998) concluíram que entre os fatores inibidores da liberação de LH (hormônio luteinizante) após parto, se inclui a amamentação associada à demanda metabólica da lactação, nutrição inadequada e/ou condição corporal precária.…”

Induction of fertile estrus during seasonal anestrus in ewes and fall born ewe lambs

“…However, flushing with lupin grains significantly decreased the ovulatory response in ewes on a long-term low plane of nutrition (Oldham and Fisher, 1992). Fogarty et al (1992) observed a decline in estrous response and an increase in the interval from lambing to first estrus in flushed ewes of -0.2 % and 1.3 days, respectively per kg gain in live weight.…”