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Effects of the level of early productivity on the lifespan of ewes in contrasting flock environments
- F. Douhard, N. B. Jopson, N. C. Friggens, P. R. Amer
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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
- K. J. Hammond, S. O. Hoskin, N. B. Jopson, C. G. Mackintosh, G. Hofstra, B. R. Thompson, D. R. Stevens
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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.
Effects of growth hormone administration on the body composition and hormone levels of genetically fat sheep
- S. M. Francis, N. B. Jopson, R. P. Littlejohn, S. K. Stuart, B. A. Veenvliet, M. J. Young, J. M. Suttie
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- Animal Science / Volume 67 / Issue 3 / December 1998
- Published online by Cambridge University Press:
- 02 September 2010, pp. 549-558
- Print publication:
- December 1998
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Coopworth sheep selected for low (lean) or high (fat) backfat have large differences in plasma GH profiles. Fat genotype ram lambs (5 months old) were treated with growth hormone (GH) to simulate the plasma GH profiles of lean sheep and investigate whether exogenous GH could modify carcass fatness. For 77 days, bovine GH was administered at 25 Uglkg live weight per day either as a single, daily subcutaneous bolus (fat bolus) or via portable pulsatile infusion pumps (fat pump) which delivered GH solution at 90-min intervals into a jugular catheter. Measurements of body composition were made by computed tomography (CT) and ultrasonic scanning during the trial, with linear carcass measurements and proximate analysis undertaken at the end of the experiment.
Before treatments began, mean plasma GH levels were lower (P < 0·01) in fat control (0·34 ugll) than in lean lambs (1·1 μg/l). Several weeks after the start of the trial, mean plasma GH had increased in both fat bolus (1·2 μg/l) and fat pump (0·45 μg/l) treatment lambs with major changes in the pulsatility relative to the fat control lambs. Although these changes were maintained in the fat bolus lambs, by the end of the trial there was no significant difference in mean plasma GH between fat pump and fat control sheep. Throughout the trial, plasma 1GF-1 levels were higher in fat bolus, fat pump and lean lambs than in fat control lambs. Analysis of body composition data over the GH treatment period revealed that the slope of the allometric equation for total fat relative to empty body weight was lower in the fat bolus lambs (1·07) than in the lean lambs (1·50) with fat control and fat pump treatment lambs intermediate (1·30 and 1·36, respectively). Subcutaneous fat was later maturing in lean lambs than in fat control and bolus treatment lambs when regressed against total fat, with the fat pump treatment lambs being intermediate. Linear carcass measurements revealed changes due to GH administration in the distribution of subcutaneous fat and eye muscle dimensions.
It is concluded that sheep from the fat genotype show physiological responses to exogenous GH. Increasing plasma GH levels of fat sheep increased plasma IGF-1 and had variable effects on carcass fatness. The change in body composition may be affected by the mode of administration of exogenous GH.
Tissue mobilization rates in male fallow deer (Dama danta) as determined by computed tomography: the effects of natural and enforced food restriction
- N. B. Jopson, J. M. Thompson, P. F. Fennessy
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- Journal:
- Animal Science / Volume 65 / Issue 2 / October 1997
- Published online by Cambridge University Press:
- 02 September 2010, pp. 311-320
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- October 1997
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The breeding season in temperate species of deer is characterized by the rut, a period of intense sexual activity when the male eats very little and competes for access to females. Males have been reported as losing proportionately up to 0·30 of live weight over a 6- to 8- week period. The majority of the live-weight loss is accounted for in loss of depot fat, with smaller losses in muscle reserves. The effects of body composition, hormone status and season on these changes in fat and muscle reserves were examined in mature fallow bucks (Dama dama).
The experiment was conducted in two stages, the ‘rut’ (February to May), and ‘spring’ (June to November). For the ‘rut’ period, bucks were randomly allocated to either ad libitum feeding, entire (HiEnt), matched group feeding, castrated (CAST), or entire bucks restricted to 7·6 kg dry matter per week (LoEnt) treatment groups (no. =4, 4 and 6, respectively). Three bucks from each of the HiEnt and LoEnt groups were selected for the ‘spring’ period. Bucks were given food ad libitum until mid October, whereupon they were restricted to 2·5 kg dry matter per week for 4 weeks (SPRING). Group food intake and individual live weights were measured weekly throughout both, periods. Body composition was measured by computed tomography on five and three occasions during the ‘rut’ and ‘spring’ stages, respectively.
Comparisons of the relative losses of total fat and muscle relative to empty body weight (EBW) using the allometric model (y = aXb) revealed significant treatment differences. HiEnt bucks had a high relative rate of fat and a low rate of muscle mobilization (b = 5·23 and 0·38, respectively). Only the CAST group had lower (P < 0·1) b coefficient for fat than the HiEnt group at 2·79. The LoEnt group was the only group in which the b coefficient for muscle (at 1·07) was not significantly lower than 1·0. Visceral organ weight was lost at the same rate as EBW across all treatments. There was no net loss or gain of bone for any treatment group as the b coefficients were not significantly different from zero. Fat depots were analysed relative to the total fat depot using the allometric model. The HiEnt group displayed a pattern of fat mobilization whereby the external depots were mobilized at the greatest relative rate and the internal fat depots at the lowest rate (b coefficients were 1·86, 1·23 and 0·68 for the subcutaneous, intermuscular and internal fat depots, respectively). CAST and SPRING groups were not significantly different from HiEnt bucks in the relative mobilization of fat depots. All fat depots in the LoEnt group were mobilized at the same relative rate as total fat, as the b coefficients were not significantly different from 1·0.