Ewe size, pregnancy nutrition and pregnancy rank are known to affect the productive performance of ewes and their offspring. The aim of the present study was to compare the effects of two nutritional regimens, from day 21 to day 140 of pregnancy, in singleton-and twin-bearing ewes of two different mean weights, taken from a single flock. The study included Large ewes offered Ad lib (Large-Ad lib, n= 151), Large ewes offered Maintenance (Large-Maintenance, n = 153), Small ewes offered Ad lib (Small-Ad lib, n = 155) and Small ewes offered Maintenance (Small-Maintenance, n = 153) that were either singleton-or twin-bearing. During the period day 21 to day 140 Maintenance and Ad lib feeding regimens included Large and Small ewes and singleton-and twin-bearing ewes. At days 1 and 140 of pregnancy Large ewes were heavier (P < 0.05) and of greater (P < 0.05) body condition than Small ewes. Similarly, at days 1 and 140 of pregnancy twin-bearing ewes were heavier (P < 0.05) than single-bearing ewes. At day 1 of pregnancy there was no difference in ewe liveweight and body condition scores between Maintenance and Ad lib-fed ewes, but by day 140 ewes in the Ad lib regimen were heavier (P < 0.05) and had greater (P < 0.05) body condition than Maintenance ewes. There was an interaction (P < 0.05) between ewe nutritional regimen and lamb birth rank for lamb birth weight such that twin lambs born to Maintenance regimen ewes were lighter (P < 0.05) than their counterparts born to Ad lib ewes (4.52 ± 0.06 versus 5.23 ± 0.06 kg respectively). This relationship was not observed in singletons. There was also an interaction (P < 0.05) between ewe size and nutritional regimen for lamb birthweight. Birth weights did not differ between lambs born to either Small or Large ewes on the Ad lib feeding regimen. However, lambs born to Small ewes on the Maintenance feeding regimen were lighter (P < 0.05) than their counterparts born to Large ewes (5.09 ± 0.07 versus 5.37 ± 0.07 kg respectively). At day 100 of lactation lambs born to Large ewes were heavier (P < 0.05) than those born to Small ewes (32.65 ± 0.37 versus 31.16 ± 0.35 kg respectively) and those born to Ad lib ewes were heavier (P < 0.05) than those born to Maintenance ewes (32.77 ± 0.37 versus 31.03 ± 0.36 kg respectively). This study shows that level of dam pregnancy nutrition has a greater effect on twin-born lambs than their singleton-born counterparts. Furthermore, the data suggests that the heavier liveweights at weaning of lambs born to Large ewes may not have compensated for their dams' greater nutritional requirements compared to their smaller counterparts.

Fetal growth is normally constrained by maternal factors. This constraint is demonstrated by the usual inverse linear relationship between litter size and mean fetal weight. Cross-breeding experiments between mice of lines selected for high or low plasma insulin-like growth factor (IGF-I) levels suggested that elevations in maternal IGF-I abolish (P less than 0.01) this constraining effect and reverse the usual positive relationship between fetal and placental size in late gestation. This was confirmed by treating mice and rats throughout pregnancy with IGF-I. In normal mice and in low IGF-I line mice treatment with IGF-I (10 micrograms 8-hourly s.c. from day 1 to 19 of pregnancy) abolished maternal constraint whereas 0.9% (w/v) NaCl treatment did not. In Wistar rats osmotic pumps were implanted to deliver IGF-I (1 microgram/g body weight per day), bovine GH (bGH; 0.6 microgram/g body weight per day) or saline from day 1 to 19 of pregnancy. IGF-I therapy but not bGH or saline abolished (P less than 0.01) maternal constraint and altered (P less than 0.01) the relationship between placental and fetal weight. When high or low IGF-I line mice embroys were transplanted into a normal line of mice, the expected negative relationship (P less than 0.05) between mean fetal weight and litter size was maintained. However, the embryos of the high line were heavier (P less than 0.05) than those from the low line irrespective of fetal number, suggesting a direct role for IGF-I in the regulation of fetal growth.(ABSTRACT TRUNCATED AT 250 WORDS)

Data from a selection experiment conducted with sheep at Massey University, New Zealand, were analyzed to obtain an evaluation of selection response. Selection was for heavy 14-mo greasy fleece weight. Approximately seven generations of selection were represented in the data. Three estimates of genetic superiority of the selected line to the control line were obtained. All three estimates were obtained from a mixed model evaluation using the individual animal model for predicting breeding values from own and relatives' records. The estimators were 1) deviation of selected line predicted yearly phenotypes from control line predicted yearly phenotypes, 2) deviation of the predicted yearly phenotype for the selected line from the year estimate in the control line and 3) the mean yearly breeding value from the analysis of the selected line only. The realized heritability using the first approach was .20. However, the control line was found to have a slight positive drift; hence, this estimate was biased downward. Using Approach 2, accounting for drift, the realized heritability was .23. The same realized heritability, .23, was obtained from an analysis of the selected line ignoring the control (Approach 3), when a prior heritability of .30 was assumed for the mixed model evaluation. The estimate of genetic trend from predicted breeding values in the latter approach is, however, quite dependent on the assumed heritability.

No abstract

Greater rates of genetic gain can be achieved by selecting animals born to younger parents. However, little is known about the lifetime performance of dual purpose ewes (Ovis aries) that are born to primiparous ewe lambs (8 to 9 months old at breeding). This experiment investigated the effect of being born from either a ewe lamb or mixed age dam as either a single or twin on the lifetime performance of ewe progeny. Lifetime performance was measured in terms of the life time live weights of the ewes, the weight and number of lambs born and weaned, the efficiency of production (kilograms of lamb weaned / predicted pasture intake (kgDM) of the ewes), and ewe survival. The study followed the lifetime production of 17 single and 41 twin female lambs born to mature ewes (M1 and M2, respectively), and 28 single and 29 twin lambs born to ewe lambs (L1 and L2, respectively). Over their lifetime L2 ewes were lighter (P<0.05) but had similar body condition scores to the other three ewe groups. There was no difference in average progeny weaning weight or total progeny litter weaning weights between groups. The M1 ewes had the greatest longevity (P<0.05) of the four groups. Even though L2 ewes were lighter than the other three groups, this was insufficient to increase their lifetime efficiency of production (kg lamb weaned/predicted pasture consumption), relative to the other groups. These results suggest farmers could select replacements born to ewe lambs without sacrificing animal production.

The development of hepatic somatotrophic receptors and plasma concentrations of insulin-like growth factor-I (IGF-I) were investigated at five different ages (2, 20, 35, 105 and 165 days) in four male pigs per group. The specific binding of 125I-labelled porcine GH (pGH) to hepatic somatotrophic membranes was very low at 2 days of age (0.53 +/- 0.12%), and increased progressively (P less than 0.01) with advancing age to 3.60 +/- 0.95% at 165 days of age. Specific binding of 125I-labelled bovine GH (bGH) to the same membrane preparations was markedly higher than binding of 125I-labelled pGH; it also showed a distinct developmental increase (P less than 0.01) with age from 4.4 +/- 0.55% at 2 days of age to 24.0 +/- 1.90% at 165 days of age. Plasma concentrations of IGF-I increased significantly (P less than 0.01) from 79 +/- 14.0 micrograms/l at 2 days of age to 610 +/- 64.0 micrograms/l at 165 days of age. Non-linear regression analysis of the competitive binding data using bGH as labelled and unlabelled ligands showed linear Scatchard plots in the three youngest age groups, with an association constant (Ka) of approximately 3.5 litres/nmol. Curvilinear Scatchard plots were observed in the two oldest age groups. The Ka for the higher affinity binding site (approximately 5.0 litres/nmol) was very similar to that for the sole site observed in the younger animals. The Ka of the lower affinity binding site was approximately 0.35 litres/nmol.(ABSTRACT TRUNCATED AT 250 WORDS)

Herbage organic matter intake (OMI), grazing behaviour and ewe and lamb production were measured during the last 4 weeks of pregnancy in 2-year-old and mixed-age Border LeicesterxRomney ewes due to lamb in June (winter) or August (spring). The intake of herbage (averaged across lambing date groups) was 1.4�0.1, 1.71�0.1, 1.7�0.1 and 1.9 9�0.1 kg OM ewe-1 day-1 (mean � s.e.m., P < 0.01) for ewes continuously stocked on 10-year-old ryegrass (L. perenne) and white clover (T. repens) pastures maintained at sward surface heights (SSH) of 2.0, 4.0, 6.0 and 8.0 cm respectively. Ewes that were in a good body condition score achieved their required daily intake of energy at a SSH of 2.0 cm. Relative to ewes on the 8.0 cm SSH treatment, those on the 2.0, 4.0 and 6.0 cm SSH treatments attempted to increase intake by increasing grazing duration rather than biting rate. Ewe liveweight, condition score, midside wool growth rate and mean fibre diameter were not affected by sward surface height in either lambing group. There was no within season effect of SSH on lamb birthweight, but lambs born in June were lighter than lambs born in August (4.4k0.2 v. 5.3�0.2 kg, P < 0.001). This trial has shown that, at the same SSH, June-lambing pregnant ewes achieve a similar daily herbage intake to that of August-lambing ewes. A target SSH of 2.0 cm during the last month of pregnancy was shown to be appropriate for both August- and June-lambing ewes in good condition. However, for August-lambing ewes in poor condition, a SSH of 2.0 cm at this stage of pregnancy would be detrimental to overall production, particularly in terms of ewe liveweight loss.

Chondrodysplasia in Texel sheep is a recessively inherited disorder characterized by dwarfism and angular deformities of the forelimbs. A genome-wide association study using the Illumina OvineSNP50 BeadChip on 15 sheep diagnosed as affected and eight carriers descended from three affected rams was conducted to uncover the genetic cause. A homozygous region of 25 consecutive single nucleotide polymorphism (SNP) loci was identified in all affected sheep, covering a region of 1 Mbp on ovine chromosome 4. Seven positional candidate genes - including the solute carrier family 13 (sodium/sulphate symporters), member 1 (SLC13A1) - were identified and used to search for new SNPs for fine mapping of the causal locus. The SLC13A1 gene, encoding a sodium/sulphate transporter, was the primary candidate gene attributable to similar phenotypes observed in the Slc13a1 knockout mouse model. We discovered a 1-bp deletion of T (g.25513delT) at the 107 bp position of exon 3 in the SLC13A1 gene. Genotyping by direct sequencing and restriction fragment length polymorphism analysis for this mutation showed that all 15 affected sheep were g.25513delT/g.25513delT; the eight carriers were g.25513delT/T and 54 normal controls were T/T. The mutation g.25513delT shifts the open reading frame of SLC13A1 to introduce a stop codon and truncate C-terminal amino acids. It was concluded that the g.25513delT mutation in the SLC13A1 gene was responsible for the chondrodysplasia seen in these Texel sheep. This knowledge can be used to identify carriers with the defective g.[25513delT] allele to avoid at-risk matings to improve animal welfare and decrease economic losses.