Abstract
The objectives of this study were to estimate the phenotypic correlations of residual feed intake (RFI) and gross feed efficiency (GFE) with hematological and metabolic blood profiles of lambs and to determine the differences for these traits in animals of different RFI classes. Twenty Ile de France male lambs, 115±8 days of age and 31.3±4.1 kg of body weight (means ± SD), were individually housed and their dry matter intake was measured over 65 days. They were weighed every 13 days to determine the average daily weight gain and two blood samples were collected at the last two weighings (at 07h30) for analysis of blood variables. The animals were divided into two classes: negative RFI (most efficient: <0.5 SD below the mean; n = 6) and positive RFI (least efficient: >0.5 SD above the mean; n=8). There were associations among RFI and the serum metabolic variables for albumin (rRFI = 0.74) and creatinine (rRFI = -0.45) and between GFE and serum albumin (rGFE = -0.70). Less efficient animals as measured by RFI had higher serum albumin and lower creatinine levels and showed a tendency to have a greater concentration of total plasma protein. Other serum biochemical parameters were not correlated with GFE and RFI, and no differences between RFI classes were found. There was a correlation between the percentage of eosinophils and RFI (rRFI = -0.65), and such more efficient animals had a higher proportion of these cells and a trend to have a lower percentage of monocytes. This study provided evidence indicating associations between RFI and protein metabolism, as reflected by the serum albumin and creatinine. The hematological findings suggest that RFI is related to susceptibility of lambs to stressand should provide a basis for further research in this regard.
Highlights
Feed is often one of the most expensive items in sheep breeding cost analyses (Barros et al, 2009)
This study provided evidence indicating associations between residual feed intake (RFI) and protein metabolism, as reflected by the serum albumin and creatinine
Among other measures that have emerged over the years for the evaluation of animal feed efficiency, residual feed intake (RFI) was proposed for beef cattle mainly because it is not directly correlated with the rate of gain and body weight (BW), which is important because these latter traits can affect feed requirements (Arthur et al, 2001)
Summary
Feed is often one of the most expensive items in sheep breeding cost analyses (Barros et al, 2009). The feed efficiency of animals has an important influence on the profitability of production systems and provides the potential to identify and select animals with an improved ability to convert feed into animal product. Improved efficiency of livestock plays an important role in reducing their environmental impact because the grazing areas needed for livestock can be reduced, and waste production, such as manure and methane, may decrease with a better use of diet (Basarab et al, 2003). Gross feed efficiency (GFE) can be interpreted as the effectiveness of converting ingested feed into products. Among other measures that have emerged over the years for the evaluation of animal feed efficiency, residual feed intake (RFI) was proposed for beef cattle mainly because it is not directly correlated with the rate of gain and body weight (BW), which is important because these latter traits can affect feed requirements (Arthur et al, 2001). Residual feed intake is defined as the difference between the observed feed consumption and the estimated feed consumption of an animal, the more negative the residual portion is, the greater the feed efficiency of an animal
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