Year: 1991
Type: article
Abstract: Summary. The effect of maintaining female sheep at a body weight intermediate between the normal weight for puberty (30–35 kg) and 20 kg (puberty suppressed) on the onset of oestrous cycles was studied. In addition, the influence of ad-libitum food intake or insulin infusion was studied in animals previously maintained at 20 kg. Coopworth ewe lambs (10 weeks old) were allocated to one of 6 treatments: (A) ad-libitum fed (n = 6), (B) ad-libitum fed to 28 kg then maintained at that weight (n = 6), (C) ad-libitum fed to 24 kg then maintained at that weight (n = 6), (D) maintained at 20 kg until Week 29 and then fed ad libitum (n = 6), (E) maintained at 20 kg and infused with 0·1 U insulin/kg/24 h for 2 weeks from 29–31 weeks of age (n = 5), (F) maintained at 20 kg (n = 6). The lambs were penned indoors under natural photoperiod, which was decreasing virtually throughout the study, and fed a pelleted concentrate diet which was recorded daily. They were blood sampled twice a week, and plasma was analysed for progesterone. Puberty was defined as the date when plasma concentrations of progesterone first exceeded 1 ng/ml. In addition, ewes in Groups D, E and F were blood sampled every 10 min for 8 h on Days 0 and + 12 of the insulin infusion or access to ad-libitum feeding and the plasma was analysed for luteinizing hormone (LH). All ad libitum-fed lambs in Group A exhibited puberty at a mean (± s.e.m.) age of 26·1 ± 1·8 weeks and a weight of 44·2 ± 2·4 kg. Puberty was delayed 5 weeks in Group B lambs and occurred after the food required to maintain weight at 28 kg had been reduced from ∼ 8 kg/week to 4 kg/week. The animals in Groups F (20 kg), and C (24 kg) did not reach puberty by 38 weeks of age, when photoperiod was increasing and thus was inhibitory for puberty. The insulin infusion (Group E) was without effect on LH or progesterone secretion but ad-libitum nutrition (Group D) caused an increase in LH secretion 6 days later and puberty in 4 of the 6 lambs 5 weeks later. It is considered that body weight per se is not a primary cue for puberty in sheep, but animals at an intermediate weight can adapt to undernutrition and achieve puberty. The mechanism of adaptation to undernutrition is not known but is unlikely to be due to a modest increase in blood insulin concentrations. Keywords: puberty; ewe lamb; body size; food intake; growth restriction; metabolic adaptation
Source: Reproduction
Institutions: University of Michigan, Michigan Medicine
Language: English
Subfield: Agronomy and Crop Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: bronze
OpenAlex ID: W2149187704