Early Lamb Research Articles

Genetic trends over 20 years of selection in the three synthetic Arcotts, Suffolk and Finnish Landrace sheep breeds. 1. Early growth traits

Mixed model methodology based on a multi-trait animal model was used to estimate genetic trends for lamb weights in three synthetic Arcott (Canadian Outaouais and Rideau) breeds and two random bred control (Suffolk and Finnish Landrace) breeds. Selection in the Canadian Arcott was primarily on lamb weight at 91 d with a lesser emphasis on litter size. Outaouais and Rideau Arcotts were selected primarily for litter size with a lesser emphasis on lamb weight at 91 d. All lambs were housed indoors year-round in a controlled environment under conditions of artificial rearing and 8-mo breeding cycles. Genetic improvement over 20 yr based on predicted breeding values for lamb weights at birth, 21, 70 and 91 d of age were 0.3, 0.9, 2.1 and 2.8 kg, respectively in the Canadian, 0.2, 0.6, 1.2 and 1.5 kg in the Outaouais, and 0.3, 0.5, 0.9 and 1.4 kg in the Rideau breeds. Corresponding values for the unselected Suffolk were 0.3, 0.4, 0.4 and 0.5 kg, respectively, and for the Finnsheep were 0.2, 0.2, 0.3 and 0.5 kg. Alternative methods of estimating genetic trends using control populations were based on deviation of the predicted mean year-season phenotype in the selected breeds from that in the corresponding random bred control breeds (Suffolk for Canadian, and Finnsheep for Outaouais and Rideau) and also as a deviation from the year-season estimate in the corresponding random bred control breeds. Genetic trends estimated from the alternative methods, which took into account the contribution of drift, were larger than those based on predicted breeding values. These values were reflected in the realized heritabilities estimated from regression of cumulative selection differential on the genetic trends. In the Arcott breeds, annual genetic trend for lamb weights varied according to breed and the estimation procedure which amounted to 0.25–0.81% of the mean. It is evident selection offers one of the most practical means for rapid and permanent improvement of early lamb growth in multi-breed synthetic populations under conditions of artificial rearing, 8-mo breeding cycle and a controlled environment. Key words: Sheep breeds, genetic trends, multi-trait animal model and growth traits

A genetic analysis of early growth and ultrasonic measurements in hill sheep

AbstractGenetic parameters were estimated for early lamb growth and ultrasonic measurements taken on Scottish Blackface lambs reared under extensive conditions on two Scottish hill farms. Measurements were taken on approximately 2000 lambs born to unselected ewes, and sired by 32 rams previously selected for divergent predicted carcass lean content. Heritabilities for birth weight, marking iveight (at approx. 6 weeks of age) and weaning weight (at 17 weeks) were 0·07 (s.e. 0·04), 0·02 (s.e. 0·03), and 0·14 (s.e. 0·05), respectively. Heritabilities for ultrasonic muscle and fat depths at weaning were 0·27 (s.e. 0·09) and 0·16 (s.e. 0·06), respectively. There was a strong maternal effect on weight which declined from birth with lamb age and was relatively unimportant for the ultrasonic measurements. The rearing environment of the lambs (hill pasturev.‘improved’ (or ‘inbye’) pasture) was an important environmental effect on the heritability estimate for backfat thickness, with that for lambs reared on improved pasture being twice that of hill-reared lambs. The implications of the results from this work on genetic improvement of sheep in liill environments are discussed.

Genetic progress in the lleyn group breeding scheme using a multitrait selection index

Group breeding schemes were introduced into Britain in the 1970s as a means of increasing the rate of genetic improvement in sheep and providing a vehicle for breeders to cooperate and pool resources. The Lleyn Group Breeding Scheme was set up in 1978 with the aim of improving several maternal traits in a breed known for its prolificacy. Although the breed originates from North Wales members of the group were drawn from different parts of Britain. Flocks in the scheme were all recorded by MLC and sheep had the possibility of being selected using MLC's selection index, appropriately weighted for the traits of interest to group members.This analysis was designed to investigate the genetic progress made in the scheme between 1979 and 1993. Three traits were analysed; adjusted early lamb weight (LW) (at eight weeks of age), mature weight (MW) (at 18-months) and litter size (LS) in the form Number of lambs born per ewe lambing (NLBEL). These three traits were investigated in ten flocks which participated in the scheme, at varying levels, during the 14-year period 1979-1993. However, only genetic progress in the nucleus flock is reported in this paper.

The effects of restricting concentrate intake on january born lambs at grass

In an early lamb production system feed costs and age at slaughter are big factors in determining profit. Farmers are being forced to become more efficient producers as costs of production continue to rise and farm product prices fail to keep pace with inflation. The aim of this experiment was to evaluate the performance of lambs fed concentrates ad-libitum to those fed to a maximum restricted level of 0·5 kg/hd/day.

The effects of restricting concentrate intake on january born lambs at grass

In an early lamb production system feed costs and age at slaughter are big factors in determining profit. Farmers are being forced to become more efficient producers as costs of production continue to rise and farm product prices fail to keep pace with inflation. The aim of this experiment was to evaluate the performance of lambs fed concentrates ad-libitum to those fed to a maximum restricted level of 0·5 kg/hd/day.

Genetic progress in the lleyn group breeding scheme using a multitrait selection index

Group breeding schemes were introduced into Britain in the 1970s as a means of increasing the rate of genetic improvement in sheep and providing a vehicle for breeders to cooperate and pool resources. The Lleyn Group Breeding Scheme was set up in 1978 with the aim of improving several maternal traits in a breed known for its prolificacy. Although the breed originates from North Wales members of the group were drawn from different parts of Britain. Flocks in the scheme were all recorded by MLC and sheep had the possibility of being selected using MLC's selection index, appropriately weighted for the traits of interest to group members.This analysis was designed to investigate the genetic progress made in the scheme between 1979 and 1993. Three traits were analysed; adjusted early lamb weight (LW) (at eight weeks of age), mature weight (MW) (at 18-months) and litter size (LS) in the form Number of lambs born per ewe lambing (NLBEL). These three traits were investigated in ten flocks which participated in the scheme, at varying levels, during the 14-year period 1979-1993. However, only genetic progress in the nucleus flock is reported in this paper.

Effects of postpartumTrypanosoma vivaxinfection on feed intake, livevveight changes, milk yield and composition in West African Dwarf ewes and associated lamb growth rates

SUMMARYThe effects of trypanosomiasis on digestible organic matter intake, milk yield and composition, dam liveweight changes during lactation and lamb growth rates were investigated at Ibadan, Nigeria 1991/92, using 20 West African Dwarf sheep nursing single lambs. Although digestibility coefficients were neither affected by infection nor by level of feed intake, organic matter intake during early and late lactation was significantly lower in infected dams. Nitrogen retained in late lactation was lower in infected animals due to reduced feed intake. Mean daily milk yields were not affected by the infection during early lactation; however, during the second half of lactation, average daily milk yields were significantly lower in infected animals than in uninfected controls. Variations in milk component concentrations between experimental groups did not attain statistical significance throughout lactation. While control ewes on a high plane of nutrition (CH) gained 12·1 g/day, infected ewes (IH) and uninfected control ewes on a medium plane of nutrition (CM) lost 45 and 5·4 g/day respectively during lactation. Liveweight gain in the lambs was not affected by infection in the dams.This study demonstrated reduction in feed intake, late lactation milk yield and dam liveweight gain with no adverse effect on digestibility coefficients, milk composition, early lactation milk yield and lamb weight gain duringT. vivaxinfection of lactating ewes.

Ryegrass endophyte and sheep reproduction

The influence of perennial tyegrass endophyte on sheep reproduction and early lamb growth was studied in a 3-year grazing experiment at the AgResearch regional station at Gore (46"07'S, 168"54'E). The trial consisted of 8 paddocks sown in endophyte-infected (+E) or endophyte-free (-E) Grasslands Nui perennial ryegrass, with (+C) or without Grasslands Huia white clover. Endophyteinfected ryegrass delayed the lamb drop and reduced lamb weight gains during the lactation period. Lamb drop was delayed by an average of 3-5 days especially in the presence of clover. This may be due to an extended gestation period or delayed mating. There was no effect of endophyte on lamb birth weight, ewe conception rate and liveweight changes over autumn, winter and spring. Keywords: Acremonium l&i, lambing time, liveweight change, Lolium perenne, sheep reproduction, Southland

Factors affecting vitamin a concentration in lambs liver

A number of recent reports relating to human health have suggested that pregnant women should limit their consumption of sheep's liver because of the possible dangers of hyper-vitaminosis from high vitamin A levels in this organ. Foetal defects, especially in early pregnancy, have been mentioned (Dept. of Health, 1990; Ilback, Busk, Halen & Slorach, 1991) as possible dangers resulting from high consumption of vitamin A.Since the introduction of the sheep meat regime in 1980, under CAP, the output of early lamb production in Ireland has increased significantly. As early lamb has traditionally been a high priced product, geared towards the Easter market, high lamb performance is a high priority. This invariably necessitates high feed inputs in the form of concentrate feed. For various reasons, most commercial concentrates have added vitamina A levels higher than is necessary to meet animal requirements. It has been suggested that this source of vitamin A may be responsible for elevated vitamin A levels in the liver. Consequently, the aims of the present experiment were to quantify the vitamin A status in lambs liver selected from scientifically controlled production systems and to relate the values to lamb sex and age.

Stimulation of seasonally anovular mule ewes by rams

Early lamb production is a specialist enterprise in which profitability is highly dependent on getting all the lambs sold while prices are still high in Spring when lamb is in short supply. This involves lambing in late December/early January. Hence ewes must be mated in August. Conventionally in the UK, this has been achieved by the use of progesterone-impregnated sponges and pregnant mare's serum gonadotropin (PMSG). The ram effect is a powerful technique for the control of sheep reproduction. The objective of the present study was to reinvestigate the value of teasers for the stimulation of seasonal activity in the ewe.125 (2-3 yr) Mule ewes (Blue-faced Leicester x Swaledale or Blackface), isolated from rams for two months, were used to investigate the effect of different durations of teasing on the stimulation of seasonal activity. Groups of 25 ewes were exposed to either teaser vasectomised rams and teaser ovariectomised ewes (induced into behavioural oestrus by an intramuscular injection of 0.2 mg of oestradiol benzoate) for 1 month (group l), 3 weeks (group 2) and 2 weeks (group 3); or vasectomised rams only for 2 weeks (group4); or left untreated (group 5). At the imposition of treatments, groups were isolated from each other and from contact with other 3heep by a distance of at least 1 km. Plasma progesterone was measured twice weekly on 8 animals, per group to determine ovarian activity.

Use of intrarumlnal soluble glass boluses containing two levels of melatonin for early lamb production

It has been shown that giving mule ewes a soluble glass bolus which contained 150 rag melatonin on 2 July, advanced the onset of the oestrus cycle. This experiment was designed to investigate whether the dose rate of melatonin could be reduced.1.40 ewes not treated (control).2.40 ewes given glass bolus containing 150 mg melatonin.3.40 ewes given glass bolus containing 100 mg melatonin.120 mule ewes (Blue-faced Leicester x Swaledale) aged between 4 and 6 years all of proven breeding ability were divided into 3 similar groups by age, weight and body condition on 2 July. One group was left untreated and 2 groups received a polymer-bonded soluble phosphate glass bolus (Pilkingtons P.L.C.) which contained the appropriate level of melatonin (Sigma Chemicals Corporation). Each bolus was cylyndrical in shape measuring 1.8 cm in diameter and 3.0 cm in length. Tho average mass and specific gravity of boluses were 23 g and and 3.0 respectively.

Use of an intraruminal soluble glass bolus containing melatonin for early lamb production.

The use of melatonin to advance the onset of seasonal oestrus is potentially useful for early lamb production. A number of delivery systems for melatonin have been developed and this study evaluates an intraruminal soluble glass bolus under field conditions. Anoestrous, non-lactating mule and Dorset cross mule ewes were treated in late June with two types of bolus of different solubilities (melatonin 1, 'slow release' and melatonin 2, 'extra slow release'). Rams were introduced in mid-August for a target lambing pattern in mid-January. The percentage pregnancy/lambing rates were 80/78, 97/92 and 100/100 in the control, melatonin 1 and melatonin 2 groups, respectively. The number of lambs born per ewe put to the ram was significantly increased by treatment with melatonin 2 (P less than 0.05) from 1.17 to 1.64 in the mule ewes and 1.64 to 1.72 in the Dorset cross mule ewes. The melatonin containing soluble glass bolus is a novel and convenient method of reducing the number of barren ewes in an early lambing flock.

The first 28 amino acids of mature LamB are required for rapid and efficient export from the cytoplasm.

Our laboratory has been utilizing the Escherichia coli outer membrane protein LamB to study the mechanism of protein localization. Various lines of evidence suggest that, in addition to a signal sequence, regions within the mature protein are required for efficient localization. In particular, studies using LamB-LacZ hybrid proteins have identified regions between amino acids 27 and 49 of mature LamB, which may play an important role in localization. To elucidate further the function of these regions, a series of in-frame deletions that remove varying lengths of early lamB sequences was constructed. The effects of these deletions on export of a large LamB-LacZ hybrid protein, 42-1, and on export of an otherwise wild-type LamB protein were determined. We find a strong correlation between the sequences deleted and the export phenotypes these deletions impart to both LamB and the LamB-LacZ42-1 hybrid protein. On the basis of these findings, the deletions can be divided into several distinct classes that define a region within mature LamB that participates in localization. This region extends amino terminally from amino acid 28 of the mature protein and functions in the rapid and efficient localization of LamB from the cytoplasm.

Prolificacy and 50-day lamb weight of ewes in the Cambridge sheep breed

ABSTRACTThe paper describes the results of the analysis of over 3000 records of Cambridge sheep kept on 11 farms over a 12-year period. The heritability of the number of lambs born per ewe increased from a low value for the 1-year-old ewes to a high value for the 3-year-old ewes; the multiple age value for 2-, 3- and 4-year-old ewes was 0·33 (s.e. 0-121). Heritability estimates for number of lambs surviving were lower, but showed the same trend of increasing values with increasing ewe age. This trend in heritability was also evident for the mean 50-day lamb weight, as a trait of the ewe, which had a multiple age value of 0·20 (s.e. 0·151). The estimates of heritability of various measures of early lamb mortality were relatively low. Date of first oestrus showed a variable heritability although the multiple age value was 0·42 (s.e. 0·149).Prolificacy was strongly correlated with various measures of early lamb mortality although the correlation with the final number of lambs weaned was positive. Prolificacy was positively correlated with the ewe's mature weight and the ewe's date of first oestrus and the genetic correlation with mean 50-day lamb weight was slightly positive.The effect of increases in prolificacy on numbers of lambs weaned was markedly curvilinear with maximum numbers of lambs weaned at an intermediate level of prolificacy.

Estrous activity in different breeds and breed crosses of sheep

Estrus was monitored in 715 straightbred and crossbred ewes during spring lactation, postweaning, summer and/or late summer breeding periods. Straightbred ewes were comprised of seven breeds, and crossbreds consisted of Rambouillet- and Finnsheep-sired ewes of the seven breeds. Estrus was detected in 5.4% of the Rambouillet and Finnsheep crossbred ewes during lactation. After weaning, the incidence of estrus was 1.1% in all crossbred and straightbred ewes. The incidence of estrus was 5.2% for all ewes during the summer period. During late summer (July 28 to August 17), 42% of all ewes showed estrus and both breed of sire and breed of dam influenced estrous activity (P<0.01). Straightbred Rambouillet, Targhee, Dorset and most Rambouillet-sired crossbred ewes showed the greatest estrous activity and could be the genetic stock of choice for early lamb production. Straightbred Hampshire, Suffolk and most Finnsheep crossbred ewes showed estrous activity later in the season. Results support the conclusion that certain sheep breeds and breed crosses show estrous activity during August, while other breeds and breed crosses begin estrous activity later and continue until March or April. Thus, lambs may be produced from January through September each year by maintaining several different breeds or breed crosses in the breeding flock.

Selection on ram 18-month weight to improve lamb growth rate

ABSTRACTThirteen pairs of Suffolk rams were selected on high and low 18-month adjusted live weight from six farms over 2 years, to establish the relationship between 18-month weight and early lamb growth. Progeny were first produced in recorded crossbred flocks (618 lambs) and then in an experimental flock of crossbred ewes (1083 lambs). Different results were obtained from the recorded and experimental flocks. The regressions of lamb 12- to 13-week weight on ram 18-month weight (within farm deviation) were 0·053 ± 0·022 kg and –0·004 ± 0·020 kg, respectively. These regressions for indirect selection correspond to ‘effective’ heritabilities for direct selection for lamb growth of 0·18 ± 0·07 and 0·02 ± 0·06 respectively. Improvement of early Iamb growth is discussed and it is concluded that selection for 18-month weight is unlikely to be a useful method.

The failure of hormone therapy to induce an early lamb crop.

The failure of hormone therapy to induce an early lamb crop.

A preliminary report on selenium and animal health in Western Australia

White muscle disease in Western Australia appears to be a sporadic disease, fundamentally related to selenium deficiency but in the main limited to young sheep subjected to other concurrent stresses. Whether the complicating stress condition acts primarily at a nutritional level or whether if affects associated endocrine or metabolic pathway is uncertain from present evidence, although it is possible that both mechanisms may be involved. The disease is restricted to the southwestern agricultural districts, having rainfalls of greater than 20 inches. A much greater than average rainfall during the early winter growth stages of subterranean clover, followed a dry August and September, was common to both years (1960 and 1961) during which WMD was first widely recognized and may be ecologically significant in winter outbreaks. There are two peaks of incidence--one in late winter and early spring, affecting young lambs running mainly on subclover pastures, and the other in the summer, affecting weaners and hoggets fed cereal stubble, hay and grain. A survey of these feeds suggests that tehy are very often low in selenium, and may frequently contain less than 0.03 p.p.m. (dry matter) which is proposed as a critical level. However, many flocks grazing pastures containing less than this amount of selenium appear healthy. Ten trials were carried out in the affected area in 1960-61 to test the effect of selenium on lamb or weaner rate of growth Only one trial produced evidence of a significant response although one other suggested that an improvement had taken place. Five trials to determine the value of selenium in improving ewe fertility and early lamb survival were also conducted. The. results of two of them suggested that some improvement could be achieved. Vitamin E also appeared useful in the fertility trials. The soil and plant selenium backgrounds, insofar as thy are known in Western Australia, are discussed in relation to the pattern of outbreaks. Certain factors in the changing agricultural practices are mentioned as probable contributors, notably an increase in sheep stocking rates and heavier application of superphosphate.

Effect of Light, Temperature, and Hormones on the Reproductive Performance of Ewes2

Five lots of 20 ewes each were used for a 3-year period to study the effects of light, temperature, light and temperature, and hormones on breeding performance and early lamb production. All lots receiving treatments had a larger number of ewes exhibiting estrus than did the controls; however, this difference was not significant. In percent ewes lambing, the best results were obtained in 1956 in lot I (light), in 1957 in lot II (temperature), and in 1958 in lot III (light and temperature). For the 3-year period the light, temperature, and light and temperature lots had a significantly higher percent of ewes lambing than the hormone lot; however, only the light and temperature lot was significantly different from the controls. In 1956, using natural service, 72% of the ewes lambed. Artificial insemination was used in 1957 and 1958 and the percent of ewes lambing decreased to 42 and 32%, respectively.