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The introduction of East Friesian (EF) genetics into commercial sheep milking herds has the potential to improve milk yield and offer a robust dam for meat lamb production systems. This study was conducted to measure the milk production, feed intake and longitudinal changes in body composition of EF × Romney (EFR) and Border Leicester × Merino (BLM) ewes over the first nine weeks of lactation. Sixteen seconds parity single-bearing EFR (n = 8) and BLM (n = 8) ewes that had been mated to a purebred EF ram were housed in individual pens from 2 weeks prior to, and until 9 weeks after, lambing and fed a commercial pelleted diet with additional chaff. Milk yield was measured twice a week using the four-hour milking interval technique after injection of oxytocin and body composition was determined by dual energy X-ray absorptiometry (DXA) at 1, 3, 5 and 9 weeks of lactation. Potential milk production was higher in EFR than BLM ewes (2.57 vs. 1.92 kg/d, P = 0.028) and declined as lactation advanced. Similarly, the yields of milk fat (P = 0.015), protein (P = 0.018) and lactose (P = 0.062) were all higher in EFR than BLM ewes and declined as lactation advanced. Energy intake increased over the first 4 weeks of the study, before reaching a plateau for the remaining 5 weeks of the study. However, there was no significant difference in energy intake or energy balance between EFR and BLM ewes. Changes in tissue energy between DXA scans were highly correlated (R2 = 0.51, P

An Hologic QDR4500A dual energy X-ray absorptiometer (DXA) was used to measure live body composition in 15 second-cross wether lambs ((Border Leicester × Merino) × Poll Dorset) aged 6–8 months (17–50 kg) and 13 mature ewes (composite terminal sire line based largely on Poll Dorset, White Suffolk and Texel breeds) (44–71 kg). After slaughter, DXA scans were also performed on the whole carcasses. Values determined by DXA including total tissue mass (TTM), lean tissue mass (LTM), fat tissue mass (FTM) and bone mineral content (BMC) for the half carcass were evaluated by comparison with chemically determined composition. In the case of BMC the relationship was with chemically determined ash content. Live weight and chemically determined lean, fat and ash were strongly related to DXA-derived values for whole body TTM, LTM, FTM and BMC, respectively (R2 = 0.999, 0.988, 0.980 and 0.977, respectively). Carcass weight and chemically determined lean, fat and ash were strongly related to DXA-derived values for carcass TTM, LTM, FTM and BMC, respectively (R2 = 0.998, 0.984, 0.986 and 0.906, respectively). However, because DXA estimates were different from chemically determined values in this sample of carcasses, they needed to be adjusted with the use of appropriate regression equations to correct the in-built algorithms used to predict human body composition. These data demonstrate the efficacy of DXA as a non-destructive method for determining the composition of the whole body and carcasses of sheep.

The concept of residual feed intake (RFI), in determining differences among animals in converting feed into body tissue, was first raised in 1963. Feed efficiency is typically calculated as a function of liveweight gain (LWG) and feed intake (FI). Historically two versions of the same model were proposed, one where FI was adjusted for liveweight (LW) and LWG, and the other where LWG was adjusted for FI and LW. Variation in LWG or FI could then be partitioned into two parts; that which is expected and can be attributed to differences in FI or LWG; and that which is the residual portion, which is the deviation from the expected value based on regression, and therefore not accounted for by differences in FI or LWG. Based on this definition, it is the residual portion which is the measure of efficiency. Both within a livestock industry and between different livestock industries there is no set model for calculating RFI. This paper evaluated four models used to calculate RFI and one model used to calculate residual LWG (RLWG) at a standard level of nutrition. They were the main model currently in use in the Australian beef cattle industry (RFIB), the original models proposed in 1963 (RFI1963; RLWG1963); a French model which included ultrasound measures of muscle and fat depth (RFIF) and the use of the Australian feeding standards to calculate predicted intake and thus RFI (RFISCA). Using feed intake, liveweight and body composition data generated from the same group of sheep (n = 52) at two ages (6 mo, 13 mo), the relative merits of each model were evaluated and compared to the other models, to determine the most appropriate model to calculate RFI for sheep. For all the models except that used to calculate RLWG, over half of the variation in FI could be explained by the model. The amount of variation in FI accounted for depended on the parameters included and the dataset, with less variation in FI explained by the specific models in the older animals. The RFIF model, which included measures of body composition, accounted for the greatest proportion of the variation in FI and as such suggests that the inclusion of body composition parameters is likely to more accurately reflect true biological efficiency.

Young merino ewes were offered a pelleted ration containing approx 15% perennial ryegrass seed, either infected or not infected with wild endophyte. Each group was split so that 10 ewes received the toxin deactivation product, Elitox®. Groups were fed indoors on treatment for 4 weeks in winter (average daily temperature, 11.5ºC). Analysis for endophyte toxins indicated intakes of 63 μg/kg LW/day ergovaline and 23 μg/kg LW/day lolitrem B. Increases in respiration rate and rectal temperature were obvious after 1 week. Respiration rate more than doubled for ewes ingesting toxin-containing wild endophyte. Differences were greater with observations taken at 9 pm, compared with those taken at 9 am. The intake and liveweight gain of ewes ingesting endophyte increased relative to those on the endophyte-free diet. Administration of Elitox®, resulted in a significant interaction: respiration rate and intake increased in the absence of endophyte, but decreased in its presence. Keywords: Merino sheep, perennial ryegrass, lolitrem B, ergovaline, Elitox®, intake, respiration rate, faecal moisture

Metabolic rate and energy consumption increase through the activation of the hypothalamic-pituitary-adrenal axis when an animal is exposed to a stressor. Residual feed intake (RFI) as a measure of efficiency has been shown to be related to exogenous adrenocorticotropin hormone (ACTH)-stimulated cortisol concentrations, which is indicative of the relationship between an animal's response to stress and the efficiency with which the energy is used for growth and production. In this study, we tested the hypothesis that sheep with low post-ACTH serum cortisol concentration relative to the other sheep in the flock have lower RFI values and lower cortisol concentrations following insulin-induced hypoglycemia. Adrenocorticotropin hormone (2.0 microg/kg body weight)-stimulated cortisol concentrations were measured in 100 sheep. The extreme responders were selected (n = 12 high cortisol, n = 12 low cortisol), and feed efficiency and body composition parameters were measured. A second ACTH challenge and an insulin challenge were administered. More efficient sheep (more negative RFI value) were found to have lower (P < 0.05) cortisol concentrations following both an ACTH challenge and an insulin challenge. Low-cortisol sheep (low response to ACTH or insulin) were found to have a lower (P < 0.05) proportion of fat tissue in comparison to the high-cortisol animals. These data clearly indicate that an animal's response to exogenous ACTH or insulin-induced hypoglycemia as a stressor is related (P < 0.05) to efficiency of energy use when measured as RFI. These data have important implications in enabling identification of animals that are superior in terms of feed efficiency and for understanding the physiological mechanisms underlying efficiency of energy use.

Residual feed intake (RFI) is a measure of feed efficiency calculated as the difference between an animal’s actual intake and its expected intake based on its liveweight and growth rate over a specified period of time (Richardson, Herd et al. 2002). The efficiency with which an animal utilises energy during growth, is dependent on a number of physiological factors including body composition and the relative proportions of lean tissue mass (LTM) and fat tissue mass (FTM), due to differences in the energy cost of depositing and maintaining these tissues. Protein or lean tissue is continually degraded and resynthesised and thus the rate at which this occurs may contribute to the variation in energy required by an animal for maintenance and growth (Archer, Richardson et al. 1999). The objective of this work was to determine the relationship between feed conversion ratio (FCR, kg feed:kg gain) and residual feed intake (RFI) with body composition in rams at six months of age (6mo), and then again in the same rams at thirteen months of age (13mo).

SUMMARY: Groups of Hereford weaners carrying naturally acquired infestations of L. vituli were allocated to a factorial experiment to examine the effect of lice treatment, sex and nutrition on growth rate during winter and early spring. Plane of ntrition was the only factor influencing growth rate over this period. In untreated groups of cattle, the plane of nutrition influenced the lice score but lice score did not influence growth rate.