Effect of food allowance on diet selectivity and intake of pearl millet (Pennisetum glaucum) stover leaves by sheep

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Abstract
The influence of food allowance or level of food excess on diet selectivity and intake by sheep given pearl millet stover leaves, and the potential feeding value of the food leftovers (not eaten) (L) were studied. Animals were given food at four levels of L (100, 300, 500 and 700 g dry matter (DM) per day). All sheep received different food allowances (A, g DM per day) and had different L/A and A/M (g DM per kg M) ratios. An additional treatment consisted of feeding the leftovers from the two highest levels of food excess to six rams to have 300 g DM of L per day. A diet supplement was given to provide sufficient rumen degradable protein and sulphur to sustain microbial activity. Variances of organic matter (OM) digestibility (OMD, g/kg) and intake (g/kg M0·75) of both DM (DMI) and digestible OM (DOMI) of the original millet leaves were analysed using L, L/A, A/M and A/M0·75as independent variables. Variation accounted for was highest when OMD was analysed as a function of L/A (R2= 0·34) and when DMI was analysed as a function of A/M (R2= 0·79) or A/M0·75(R2= 0·80). The response in OMD to varying L/A was best described by the equation OMD = 457 (s.e. 16) + 157 (s.e. 48) L/A. As L/A or A/M increased, L had a lower concentration of acid-detergent fibre and a higher in sacco OM disappearance. As A/M increased, DOMI and L/A increased following a diminishing return pattern. However, when A/M fell below 31·1 (s.e. 0·9) g DM per kg M, DOMI decreased linearly. No differences (P> 0·33) were observed for OMD between the original food (505 (s.e. 8) g/kg) and the re-fed leftovers (489 (s.e. 15) g/kg), but DOMI was lower with the latter (22•4 (s.e. 0·4) v. 20·3 (s.e. 0·8) g/kg M0˙75,P< 0·03). Results suggest that DOMI of millet stover should be determined at L/A much higher than the traditionally recommended (0·15), and support the hypothesis that farmers could benefit from feeding millet stover at high allowances to animals of high economic value and give the leftovers to less valuable or less selective stock.