Blood cell profiles of steer progeny from parents selected for and against residual feed intake

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Abstract

This study examined whether a single generation of divergent selection for residual feed intake was accompanied by differences in red and white blood cell parameters that could assist in the early identification of animals likely to perform well in a test for residual feed intake. Two cohorts of steer progeny born in 1996 ( n = 74) and 1998 ( n = 120) of parents selected for low residual feed intake (high efficiency) and high residual feed intake (low efficiency) were used. The steers grazed on pasture before feedlot entry and subsequent feed intake test. Blood samples were collected from the 1998 born cattle at pasture the day before feedlot induction, and for all cattle, at the start, middle and end of their feed intake test. Statistically significant regressions between sire estimated breeding value for residual feed intake and white blood cell count, haemoglobin level, haematocrit and percentage monocytes measured on their progeny over a feed intake test were evidence for a genetic association between these blood parameters and residual feed intake. Of the cell parameters measured in the blood samples collected from cattle at pasture before feedlot entry, only white blood cell count ( r = –0.20, P <0.05) and neutrophil count ( r = –0.29, P <0.01) were correlated with steer residual feed intake in the feedlot, none ( P >0.05) were correlated with sire estimated breeding value for residual feed intake. Cell parameters measured in the blood samples collected from cattle at the start of the feed intake test were not correlated ( P >0.05) with steer residual feed intake in the feedlot or with sire estimated breeding value for residual feed intake. It is doubtful that blood parameters in a blood sample taken at pasture before feedlot entry or at the start of a feed intake test can be used to predict residual feed intake of individual steers or sire progeny groups in feed intake tests.

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