Effect of Milk Replacer Fat Content during Calfhood and Cereal Type and Supplemental Saturated Fat Inclusion in the Finishing Ration on the Performance and Carcass Composition of Young Holstein Friesian Bulls

The objective of this study was to evaluate combined effects of (i) milk replacer (MR) fat content during rearing and (ii) cereal type and (iii) fat supplementation of the finishing ration on performance and carcass composition of young dairy bred bulls. Holstein-Friesian bull calves (n=120) offered a high (30%) or low (18%) fat content MR from 2 to 10 weeks of age after which were weaned and offered a common diet based on grazed grass and 2 kg of supplementary concentrate. At 10 months of age bulls were blocked, on their original calf rearing regimen and bodyweight, and within block randomly allocated to one of four concentrate based finishing rations composed of (i) maize (M) or barley (B) included at 70%, as fed); (ii) supplemented (PF+; 5% as fed) or not (PF-) with a rumen inert palmitate rich supplement. This resulted in eight treatment groups, arranged in 2 x 2 x 2 factorial arrangement. Animal performance and live weight measurements were recorded on fortnightly basis. Bulls were slaughtered at 16 months of age. Carcass weight (CW), kidney fat (KF), rumen fat (RF), carcass conformation (CC), fat classification (CF) and subcutaneous fat-depth (FD) were recorded at slaughter. At 48hr post-mortem subcutaneous fat color (FC) was measured and the cube roll partitioned into fat, lean and bone components. Performance and carcass traits were analyzed in accordance with the factorial nature of the design using mixed models ANOVA (PROC MIXED, SAS v 9.3) with calf rearing, cereal type and palmitate supplement as fixed effects. There were no biologically significant interactions (P > 0.10) amongst the main effects for any performance, or carcass related variables viz CW, KF, RF, CC, CF, FD or FC respectively. There was no latent effect (P > 0.10) of calf rearing regimen on carcass measurements. Similarly, no effect of cereal type in the finishing ration was recorded. Inclusion of supplemental fat significantly reduced slaughter weight (PF+ 536kg v PF-517kg; P=0.004), ADG (PF+, 1.07kg v PF-1.20kg; P=0.001), CW (PF+, 267.8kg v PF-, 280.1kg; P=0.002), CC (PF+, 4.40 v PF-, 4.91; P=0.006) and CF (PF+, 5.52 v PF-, 6.00; P=0.04). Subcutaneous FD, KF, RF and cube roll fat proportion were all reduced (P<0.05) in bulls offered supplemental fat. In conclusion, supplemental fat in the finishing diet reduced animal performance and economically important carcass traits. Additionally, no evidence of latent effects of MR fat content during calfhood on any carcass trait measured.