The effect of birth rank and age of dam on the reproductive performance of ewe replacements managed under New Zealand pastoral conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand

Selecting replacement ewes that are born to ewe lambs is an uncommon practice in New Zealand; however, there is the opportunity to increase ewe efficiency and increase the rate of genetic gain if the practice is adopted. Lambs born to ewe lambs may be lighter until up to four years of age, compared with lambs born to mature ewes, however there are few unbiased comparisons of performance. The objective of this study was to compare the reproductive performance of replacements born to either mature ewes or ewe lambs. A study with 115 singletons or twins born to mature ewes or ewe lambs, found that singletons born to mature ewes were heaviest, twins born to mature ewes and singletons born to ewe lambs were intermediate, and twins born to ewe lambs were lightest for their lifetime to eight years of age. There was no difference in lifetime lamb production among these four groups, and there was no difference in the efficiency among the ewe groups, however the power of that study may have been limited by relatively low numbers of animals. A second study utilised 1082 mature ewes and 1026 ewe lambs, bred to the same rams at the same time, producing 2701 lambs, of which, 358 lambs were selected as replacements. Lambs born to ewe lambs were lighter than lambs of the same birth rank born to mature ewes from birth until weaning and had lower rates of survival at tagging and from tagging to weaning. The relationship between the probability of survival to weaning and birth weight was quadratic, and differed for each birth-rank-by-age-of-dam cohort. Lambs born to ewe lambs, and as triplets to mature ewes have lower rates of lamb survival and growth to weaning, so farmers need to prioritise time and resources to improve these. In the third study investigating reproductive performance of replacements born to either ewe lambs or mature ewes, 135 twins born to mature ewes, 135 singletons born to ewe lambs, and 88 twins born to ewe lambs were bred (if heavier than 39 kg at breeding) as ewe lambs. Of the ewe lambs that were heavy enough to be bred, there was no difference in the number or weight of lambs produced at weaning from the three groups, but twins born to ewe lambs were less likely to reach breeding weight targets. During their second breeding (at approximately 18 months), all ewes were bred, and there were no differences in the number or weight of lambs produced at weaning. This indicates that the offspring of ewe lambs could be selected as replacements, but that farmers need to consider selecting based on weight at weaning if they intend to breed the ewe lambs at eight months of age. Further work, including an economic analysis, and continued investigation into the lifetime production and efficiency of ewes born to ewe lambs is needed. Genomic technologies are currently being used by scientists to increase the accuracy of selection of replacement animals for traits that are difficult to measure in the adolescent at the time of selection. Reproductive performance as a ewe lamb has an impact on the lifetime production of a ewe, and live weight at the time of breeding can heavily influence the likelihood of the ewe lamb becoming pregnant during her first breeding. Using ewe lambs from the second and third studies, and additional ewe lambs, five gene regions were found to be associated with live weight at eight months of age in ewe lambs, and two gene regions were found to be associated with the occurrence of pregnancy during their first breeding at eight months of age. Further investigation into these, and other, gene regions associated with reproductive traits in ewe lambs could allow the use of marker assisted selection to identify genetically superior animals. In conclusion, farmers should prioritise their time and resources to improve lamb survival and lamb growth for lambs born as triplets to mature ewes, or as any birth rank to ewe lambs. Lambs born to ewe lambs could be selected as replacement ewes, if they are heavy enough to be bred themselves at eight months of age. Lambs born to ewe lambs may be lighter than lambs born to mature ewes for their entire lifetimes, but have similar reproductive performance. There is genomic control of traits such as live weight and pregnancy occurrence in ewe lambs that needs further investigation, before genomics can be considered a practical tool for farmers when selecting their replacement ewes

The effect of maternal nutrition during mid- to late- pregnancy on ewe and lamb behaviour and the association with lamb survival : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand

Lambing percentage in New Zealand has increased by almost 30% in the last 20 years. This increase is associated with a greater percentage of twin- and triplet-born lambs which have lower survival rates than singletons. The behaviour of the ewe and her lambs has been associated with lamb survival, however, relevant data on the effect of ewe mid-pregnancy body condition score (BCS) and nutrition on ewe and lamb behaviour under New Zealand pastoral farming conditions is scarce. This research included seven experiments investigating the effects of feeding ewes, with a BCS of 2.0 to 3.0 at mid-pregnancy, either ad libitum or only sufficient to meet pregnancy maintenance requirements from mid- to very late-pregnancy, on ewe and lamb behaviour at 3 to 24 hours after birth. The association between behaviour and lamb survival was also investigated. Observations on ewe and lamb behavioural were conducted at tagging (3 to 18 hours after birth) and in a triangle pen test at approximately 12 or 24 hours after birth. The effects of ewe mid-pregnancy BCS and feeding on behaviour were somewhat inconsistent across experiments, possibly due to variations in the timing and length of feeding treatments. Feeding ewes ad libitum in comparison to pregnancy maintenance requirements did not consistently improve the maternal behaviour score (MBS) of the ewe. This is not surprising as neither of the feeding treatment groups were nutritionally restricting. There was some evidence to suggest that lambs born to ewes offered the pregnancy maintenance diet exhibited a greater need, possibly due to a weaker ewe-lamb bond than lambs born to ewes on the ad lib treatment. This need was characterised in twins, in chapter four, by greater low-pitched bleating rates and decreased time to contact, suck and follow the dam. Similar, but inconsistent results were reported in other chapters. Further, when investigating the relationship between behaviour and survival, it was found that twin-born lambs with the greater need (followed their dam more quickly) were more likely to die. The opposite relationship was found in triplet-born lambs, which may be a reflection of greater competition for milk within triplet-litters compared to twin-litters. Thus, in both twin- and triplet-born lambs following behaviour is an indicator of mortality. The practical use of this behaviour as a tool to predict lamb survival is limited

Effect of heavier live weight of ewe lambs at breeding on reproductive performance, mammary gland development and subsequent live weight : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, Massey University, Palmerston North, New Zealand

Table 3.1 (=Kenyon et al., 2014b Table 1) was removed for copyright reasons. Figure 1.2 is re-used under a Creative Commons CC-BY-NC-ND 4.0 license.Breeding ewe lambs at seven to eight months of age can increase farm profitability and ewe lifetime performance. In New Zealand, 30 to 40% of ewe lambs are bred each year with a minimum recommended pre-breeding live weight of 40 kg. Ewe lamb reproductive performance increases with breeding live weight, therefore, some farmers aim to breed ewe lambs heavier than 40 kg. Increasing ewe-lamb growth rates prior to puberty, to achieve a heavier breeding live weight could, however, impair ewe lamb mammary gland development and lactational performance. Currently, little is known about the impact of breeding heavier ewe lambs on their subsequent performance, live weight, and efficiency. The aim of this thesis was to investigate the effect of breeding heavier ewe lambs on their reproductive performance, mammary gland development and live weight over their first three breeding seasons. Ewe lambs were managed from weaning to breeding and achieved an average live weight of 47.9 ± 0.38 or 44.9 ± 0.49 kg at breeding. A growth rate of 150 g/d prior to the first breeding did not affect ewe lamb mammary gland development to the weaning of their second litter, as measured using ultrasonography. Positive relationships were found between ewe lamb mammary ultrasound measures at one year of age and the growth of their progeny to weaning. The associations between ultrasound measurements and growth of the progeny indicate that ultrasound scanning has the potential to be used as a selection technique for heavier lamb live weight at weaning. Although the live weight difference between treatments was limited to three kilograms, compared with lighter ewes, heavier ewe lambs at their first breeding showed greater fertility rate, litter size and lambing percentage but did not differ in the second and third breeding seasons. Over the first three breeding seasons, heavier ewe lambs had greater lamb production than their lighter counterparts. Ewe lamb live weight treatment had no effect on progeny performance to weaning, nor ewe efficiency over the three-year period. A positive association was found between ewe lamb breeding live weight and their mature live weight at 39 months of age. Farmers should aim to breed their ewe lambs at heavier live weights to maximise their reproductive performance as a ewe lamb and, if well managed, they can achieve increased ewe performance over the first three breeding seasons, although there would be no impact on efficiency. Before firm recommendations can be made to farmers, lifetime performance and longevity of the heavier ewe lambs at breeding needs to be examined

Freemartinism in replacement ewe-lambs of the Ripollesa sheep breed

The freemartinism syndrome affects almost all female calves born as co-twins to male calves, whereas little is known about this phenomenon in female sheep. Within this context, 1,185 ewe-lambs from the Ripollesa sheep breed were genotyped for the presence of oY1 polymorphism (a non-autosomal region of the Y chromosome). Neither ewe-lambs from single births (856) nor ewe-lambs from all-female multiple births (170) were revealed as freemartins, whereas five of 159 ewe-lambs from multiple births with male co-twins were freemartins (3.15 ± 1.38%). All freemartin ewe-lambs were confirmed by physical examination of external genitalia. The results confirm a low incidence of freemartinism from heterosexual twin pregnancies in Ripollesa sheep

Lamb Production of Targhee Range Ewes Mated to Suffolk vs. Targhee Rams

Production data on a flock straightbred Targhee ewes mated to Targhee or Suffolk rams were collected during the years of 1971 through 1975. the mean lambing percent was 93.35. The average number of lambs born per ewe exposed to rams and pere which lambed were 1.44 and 1.54, respectively. The average number of lambs weaned per ewe exposed and per ewe which lambed were 1.13 and 1.20, respectively. Crossbreeding resulted in no difference in the number of the lambs born per ewe exposed or lambing. However, Targhee ewes bred to Suffolk rams weaned approximately 1% more lambs at 90 days of age. Crossbred lambs were heavier than straightbred lambs by .97 lb. at birth, 4.7 lb. at weaning (90 days of age) 620 lb. more lamb per 100 ewes. Ewes weaning twins produced 43.8 lb. more lamb than ewews rearing a single lamb. Growth rate of male lambs appeared linear through at least 150 days of age

The Effects of Artificial Photoperiod on Age at Puberty in Fall-born Ewe Lambs

A study, conducted in two replicates, examined the effects of an artificial photoperiod on puberty in fall-born ewe lambs. Replicate I was initiated in December 2011 with prepubertal Dorset ewe lambs (n = 44). Replicate II was initiated beginning in December 2012 and included prepubertal Dorset, Suffolk x Dorset and Texel x Dorset ewe lambs (n = 52). All lambs were weighed at the initiation of each replicate and randomized to one of two treatments, control or treated, based on age, weight, breed and type of birth and rearing. Control ewe lambs were housed in a barn with exposure to natural photoperiod from December 16, 2011 until March 24, 2012 in replicate I and from December 17, 2012 until March 17, 2013 in replicate II. Treated ewe lambs were housed in a section of the same barn, but exposed to natural and supplemental light (~100 lux at lamb eye level) to produce an artificial photoperiod of 16 hours light and 8 hours dark for 14 weeks, from December 16, 2011 until March 24, 2012 in replicate I and from December 17, 2012 until March 25, 2013 in replicate II. Following completion of light treatment, each treated female received a silastic implant containing 20 mg of melatonin (Melovine), subcutaneously in the ear. Light intensity during the artificial lighting period for the treated group was measured, at random intervals, throughout the experiment and had an average value of ~100 lux, at ewe lamb eye level as measured by a Digital Light Meter (LX1010B). Growth of the lambs was monitored, as both weight and age are integral components of puberty. All ewe lambs were weighed at four time points during the study, including onset for each replicate, weaning, light termination and CIDR insertion. Ewe lambs were synchronized for estrus with the use of CIDR-G inserts, administered on May 18 of each year. On May 23 of each year CIDR implants were removed and intact fertile rams introduced. Rams were removed on June 19, 2012 or June 25, 2013 after allowing a breeding period of two opportunities for behavioral estrus. Pregnancy was determined by transrectal ultrasonography 25 days after removal of the rams. Progesterone was assayed, on all animals at four time points, using a radioimmunoassay. Plasma melatonin was assayed, in a subset of both treated and control females in replicate I prior to light termination, using an ELISA method. At light termination; treated females, in replicate I, weighed an average of 52.9 +/- 1.6 kg compared to 48.1 +/- 1.6 kg for control females (P \u3c 0.05). Extended light photoperiod increased weight gain in Replicate I, but not in Replicate II. Overall, fall-born Dorset ewe lambs (56 to 57%) conceived their first spring with no effect of the artificial photoperiod/melatonin treatment. Suffolk- and Texel-sired lambs from Dorset ewes did not have the out-of-season breeding ability seen in the purebred Dorset ewe lambs, even with the artificial photoperiod/melatonin treatment; only 2 0f 14 (14%) of Suffolk-sired ewe lambs conceived

The number of offspring weaned from ewe lambs is affected differently by liveweight and age at breeding

In this paper, we tested the hypothesis that ewe lambs that are heavier and older at breeding will wean more offspring, due to increased reproductive rate and offspring survival and lower maternal mortality. To test this hypothesis, we analyzed data from more than 11,500 maternal composite ewe lambs collected over eight years. The ewe lambs had full pedigree records including birth type, age and liveweight at breeding plus records of the birthweight and survival of their offspring and the dam. The average liveweight and age at breeding was 40.2 kg and 228 days. The reproductive rate and weaning rate responses to liveweight at breeding were curvilinear (p < 0.001), and if ewe lambs achieved 45 kg by the start of breeding, their reproductive rate and weaning rate were within 5% of their maximum. By contrast, the effects of age at breeding on weaning rate was linear and increased by 0.4% per day, despite a quadratic (p < 0.01) effect of age at breeding on reproductive rate which increased only marginally when ewe lambs were older than 8 months at breeding. Increasing liveweight (p < 0.05) or age (p < 0.001) at breeding increased survival of their offspring, however an extra 10 kg of liveweight or 30 days of age at breeding increased offspring survival by less than 5%. Both liveweight (p < 0.001) and age (p < 0.01) at breeding also influenced survival of the ewe lamb dam but survival rates exceeded 95% across the range in liveweights from 30 to 55 kg and ages from 6 to 9 months. This understanding of the trade-off between age and liveweight at breeding will assist farmers to optimize the management of their ewe lambs, given the earlier they can be bred successfully the easier they can be integrated with the breeding of the adult ewe flock the following year

Effect of Breed of Sire, Level of Postweaning Nutrition and Type of Birth (Single vs. Twin) on Lambing Performance at 12 Months of Age

One of the potential area to increase efficiency of sheep production, and thereby net return, is through an increase in the reproductive efficiency of the ewe. The practice of breeding ewes as lambs and thereby getting an additional lamb crop during a ewe\u27s lifetime offers one possibility to increase the lifetime production of the ewe. Proper growth and development of replacment ewe lambs is necessary if this practice is to become a working reality. A study was designed and initiated in the fall of 1970 to evaluate the effect of breed of sire, level of pre- and postweaning nutrition, age at first breeding and type of birth on subsequent reproductive performance of the ewe. The lambing performance at 12 months of age for the first two sets of lambs from this study will be reported in this paper

Características anuais da atividade estral em borregas lanadas e deslanadas mantidas sob condição subtropical

The increased emphasis placed on lamb production in Brazil points to the need for a better knowledge of the annual pattern of reproductive activity in ewe lambs. This study evaluates the annual estrous activity pattern of hair and wool ewe lambs raised in southeast Brazil. Estrous characteristics were recorded for 12 months in ten Santa Inês and 21 Romney Marsh and Suffolk ewe lambs. Santa Inês ewe lambs exhibited a greater length of the normal estrous cycle (14 to 19 days) than Romney Marsh and Suffolk ewe lambs (17.0 &plusmn; 0.1 days vs. 16.5 &plusmn; 0.2 and 15.9 &plusmn; 0.2 days). All the ewe lambs presented a greater number of periods of estrus per animal per month for single estrous cycles (up to 26 days) during autumn and winter. During spring and summer there was a reduction of this number but this decline varied according to the breed. For Santa Inês ewe lambs the reduction was only significant in the summer. For wool ewe lambs the reduction was significant in both seasons but was more accentuated for Romney Marsh. The Romney Marsh ewe lambs had a more restricted breeding season than Suffolk and both presented optimal estrus activity in autumn and winter. Santa Inês ewe lambs had a continuous distribution of estrous cycles along the year, although presenting a reduction in the number of estrous periods in the summer. The ewe lambs of three breeds presented characteristics of sexual immaturity, like irregular estrous cycles and silent ovulations.Em função do maior interesse pela ovinocultura de corte na região Sudeste do Brasil há necessidade de conhecer melhor o padrão anual da atividade reprodutiva das borregas. Esse estudo avaliou esse padrão anual em borregas deslanadas e lanadas criadas nessa região. A atividade cíclica reprodutiva foi avaliada durante 12 meses em dez borregas da raça Santa Inês e 21 borregas das raças Romney Marsh (11) e Suffolk (10). A duração dos ciclos estrais normais (14 a 19 dias) das fêmeas Santa Inês foi maior do que a duração observada nas fêmeas Romney Marsh e Suffolk (17,0 &plusmn; 0,1 dias vs. 16,5 &plusmn; 0,2 e 15,9 &plusmn; 0,2 dias). Todas as borregas apresentaram um elevado número de períodos de estros/animal/mês para ciclos estrais simples (até 26 dias) durante o outono e inverno. Houve redução desse número durante a primavera e o verão, mas esse declínio variou conforme a raça. Para as borregas Santa Inês essa redução só foi significativa no verão enquanto que para as fêmeas das raças lanadas, a redução foi significativa em ambas as estações e mais acentuada nas fêmeas Romney Marsh. As fêmeas dessa raça também apresentaram uma estação reprodutiva mais restrita do que as fêmeas Suffolk havendo uma concentração dos estros durante o outono e inverno para as fêmeas de ambas as raças. As fêmeas Santa Inês apresentaram uma distribuição equilibrada dos estros ao longo do ano embora tenha havido uma redução do número de período de estros durante o verão. As borregas das três raças apresentaram características de imaturidade sexual como ciclos estrais irregulares e ovulações silenciosas