Effects of the level of early productivity on the lifespan of ewes in contrasting flock environments.

Selection for high levels of prolificacy has allowed substantial improvements in the production efficiency of New Zealand (NZ) sheep farms, but the consequences on ewe lifetime performance are mostly unknown. In this study, the relationship between the level of prolificacy early in ewes' productive lives and their probability to survive later (i.e. stayability) was evaluated in two contrasting NZ flock environments. Records were obtained from 6605 ewes from four ram breeder flocks representing either a moderate (n=2) or a highly variable (n=2) nutritional environment. All ewes lambed for the first time at 2 years of age and were mated the following year. The number of lambs born during the first 2 years of productive life (NLB2-3) was used as a measure of early prolificacy. Effects of NLB2-3 on stayability to 4, 5, 6, 7 and 8 years old were analysed using logistic regression. Curvilinear effects (logit-transformed) were detected (P<0.05) until stayability to 6 years and to 8 years old in the highly variable and the moderate environment, respectively. The NLB2-3 that resulted in maximum expected stayability to various ages was 3.9 to 4.2, and 4.5 to 4.7 lambs in the highly variable and in the moderate flock environments, respectively. In addition, ewe stayability was reduced when the proportion of the litter that survived from birth to weaning (i.e. ewe rearing ability) was submaximal during the early productive life. High prolific ewes had a low rearing ability whatever the environment whereas the rearing ability of lowly prolific ewes was apparently more sensitive to the nutritional environment. The poor maternal performance of ewes with low levels of NLB2-3 led to a premature culling by breeders whereas the high early reproductive effort associated with high levels of NLB2-3 seemed to be at the cost of ewes' survival, even in the moderate flock environment. In conclusion, the flock environment influenced the level of early prolificacy beyond which ewe longevity was reduced. It is suggested that further selection for high and early prolificacy in NZ flocks is likely to impair ewes' lifetime productivity.

Gastrointestinal tract development in red deer (Cervus elaphus) calves from 1 to 12 months of age.

This study provides a detailed description of the development of the gastrointestinal tract (GIT) of farmed red deer (Cervus elaphus) calves over the first 12 months of age. GIT development was measured using a combination of computerised tomography (CT) scanning and traditional slaughter plus dissection techniques. Red deer calves of a known birth date were randomly assigned to two treatment groups. A group of five animals were repeatedly CT scanned at 31, 63, 92, 135, 207, 275 and 351 days of age to identify GIT organs and determine their volume. From a group of 20 animals, subsets of four individuals were also scanned at corresponding ages (except 135 days of age). They were immediately euthanised and dissected after CT scanning to compare CT-scanned results with actual anatomical measurements. Individual organ weights were compared with their respective organ volumes determined by CT scanning and were found to have a strong, positive relationship. The combined rumen and reticulum (RR) CT-scanned volume was compared with its volume determined by the water-displacement technique and this also showed good correlation between the two techniques (R = 0.92). The allometric growth rates of organs, relative to animal live weight gains, in descending order, were the rumen, omasum, reticulum, abomasum, caecum blind sac, kidneys, spleen and liver. The red deer GIT was continuing to grow and develop when the last measurement was taken at 351 days of age. The greatest growth of the RR, when expressed in terms of empty weight, was between 31 and 92 days of age. Compared with sheep and cattle, it appears that the red deer have a similar or greater rate of RR development up until approximately 60 to 90 days of age; however, the final increments of GIT maturity in deer may take longer to complete, with the empty weight of the RR gaining 7.5 g/day between 275 and 351 days of age. CT scanning was validated in this study as a viable technique to follow GIT development in the same animals over time, and it provided novel information on allometric organ growth. The success of CT scanning highlights the potential future use of diagnostic imaging for GIT development studies.

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 6. Bone parameters in the third metacarpal and third metatarsal bones.

AIM: To determine the effect of a known training regimen on the size and mineral content of the third metacarpal (Mc3) and third metatarsal (Mt3) bones of 2-year-old Thoroughbred horses trained on racetracks. METHODS: Mc3 and Mt3 of seven horses trained on grass and sand tracks were scanned at several sites using conventional quantitative and peripheral computed tomography (CT). Bone dimensions and density in the diaphysis and epiphysis were compared with those from seven untrained horses. Calcein label was injected in two clusters, during Weeks 9 and 12. The extent and rate of diaphyseal modelling was determined by confocal fluorescent microscopic examination of thin plane parallel sections of the mid-metacarpal region. RESULTS: Volumetric bone mineral density (BMDv) of the epiphysis was markedly higher and of the diaphysis was slightly higher in trained compared with untrained horses, but greater bone size in the trained horses had the greatest effect on an index of bone strength. Active osteons, defined as Haversian systems containing calcein label, were fewer, of smaller diameter at the time of calcein injection, and had a greater bone apposition rate in trained than in untrained horses. CONCLUSIONS: Conventional training of 2-year-old Thoroughbred racehorses over a 13-week period had a significant effect on bone size, density and strength index when compared to untrained horses. CLINICAL RELEVANCE: Bone responded rapidly to early training. The data provide reference values and sites for use in longitudinal studies of commercial training regimens.

Influence of level of nutrition during late pregnancy on reproductive productivity of red deer I. Adult and primiparous hinds gestating red deer calves.

The present study aimed to relate feed intake of red deer hinds during late pregnancy to dam body condition, foetal development and calf growth. Across 3 years, multiparous (n=33) or primiparous (n=18) hinds with known conception dates were housed in individual pens from days 150-220 of pregnancy, during which time they were each offered one of three daily allowances of pelletised rations (11 MJME/kg DM; 16% CP): high (H; ad libitum), medium (M; approximately 30% less; multiparous hinds only) and low (L; approximately 50% less). Restricted intake levels were retrospectively calculated from the mean intake of H hinds in the previous week. Hinds were returned to pasture at day 220 and calving was closely monitored. Liveweights, body condition score (BCS), and lactation score (LS) of hinds were recorded weekly from day 130 of pregnancy until calves were weaned at 12 weeks of age. Calves were tagged and weighed at birth, and subsequently weighed at 7 and 12 weeks of age. Additionally, hinds in the first year of study underwent CT scans on days 150 and 215 of pregnancy to assess compositional changes of the dam and conceptus. Mean daily ad libitum intakes of H hinds increased from 1.8 to 2.0 kg DM (0.6-0.7 MJME/kg0.75) at around day 150 to 2.8-3.2 kg DM (0.8-0.9 MJME/kg0.75) by day 220. Those of M and L hinds peaked at 1.8 and 1.6 kg DM, respectively, by day 220. This was reflected in significant treatment effects on liveweight gain and change in BCS and LS by the time of calving. CT scans indicated a significant treatment effect by day 215 on the mass of hind tissues (fat and lean) and a non-significant trend on conceptus/foetal weights. Despite apparent differences in foetal growth trajectories, there were no discernable treatment effects on sex-adjusted birth weights. However, there was an unexpectedly wide spread in calving dates that reflected considerable variation in gestation length. Furthermore, gestation length was negatively correlated with change in hind liveweight (but not BCS) between days 150 and 220 of pregnancy for all groups of hinds (P<0.05). Of three neonatal calf mortalities, none were related to overweight (dystocia) or underweight (non-viability) calves. Subsequent growth rates (g/day) of surviving calves did not reflect prior treatment of their dams, although variation in birth date influenced weights on specific dates. It is concluded from this study that while variation in nutrition to hinds during the last trimester may strongly influence foetal development, under conditions of modest feed imbalance, variation in gestation length compensates to ensure optimisation of birth weight.

Bone density in sheep: genetic variation and quantitative trait loci localisation.

Bone density (BD) is an important factor in osteoporotic fracture risk in humans. However, BD is a complex trait confounded by environmental influences and polygenic inheritance. Sheep provide a potentially useful model for studying differences in BD, as they provide a means of circumventing complex environmental factors and are a similar weight to humans. The aims of this study were to establish whether there is genetic variation in BD in sheep and then to localise quantitative trait loci (QTLs) associated with this variation. We also aimed to evaluate the relationship between fat and muscle body components and BD in sheep. Results showed that there was significant (P < 0.01) genetic variation among Coopworth sheep sires for BD. This genetic difference was correlated (P < 0.01) with body weight and muscle mass. A number of QTLs exceeding the suggestive threshold were identified (nine in total). Of these, two (chromosomes 1, P < 0.05; chromosome 24, P < 0.01) were significant using genome-wide permutation significance thresholds (2000 iterations). The position of the QTL on chromosome 24 coincided with a number of other body composition QTLs, indicating possible pleiotropic effects or the presence of multiple genes affecting body composition at that site. This study shows that sheep are potentially a useful model for studying the genetics of BD.