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.

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.

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.