The effect of rumen inert fat supplementation and protein degradability in starter and finishing diets on veal calf performance and the fatty acid composition of the meat

[摘要] ENGLISH ABSTRACT: Six groups each with six Friesian bull calves were used in this investigation and slaughteredat 20 weeks of age. Calves received a low- (LD) or high (HD) degradable protein diet, eachwith or without rumen inert fat supplementation. Two commercial fat sources were used,Morlae (m) and Golden Flake (gf), included at 2.5% of the diet. A commercial milk replacer(Denkavit) was fed at 4L for 42 days, followed by 2L until weaning at 49 days of age. Thestarter diets were fed ad lib. from day 14 to 10 weeks of age and finishing diets ad lib. from11 to 20 weeks of age. There were no significant differences in body mass gain or dry matterintake over the entire 20 week period. The feed conversion ratio (FCR) was improvedsignificantly (P=0.0032) when fat was supplemented to LD, but not to HD diets. The FCR(kg dry matter/ kg gain) ofLD, HD, LDm, HDm, LDgfand HDgfdiets were 3.45,3.44,3.07,3.81, 3.02 and 3.43, respectively. All 36 calves were used in a digestibility trial, usingchromium oxide (Cr203) as a marker, during week 18 of the investigation. Digestibilityvalues (%) for the six diets (LD, HD, LDm, HDm, LDgfand HDgf) were 61.74, 65.91, 75.44,69.00, 75.54 and 67.15 for dry matter, 61.44, 61.60, 71.33, 68.23, 75.44 and 66.12 for crudeprotein and 58.56, 66.45, 75.98, 70.92, 78.43 and 70.79 for fat, respectively. The dry matter(P=O.OOOl)and fat (P=O.OOOl) digestibilities were only significantly higher when fat wasadded to LD diets. The crude protein (CP) digestibilities were significantly higher when fatwas added to either the LD (P=0.0001) or the HD (P=0.0488) diets.All the calves were slaughtered at 20 weeks of age and the fatty acid content of the meat (m.longissimus) and subcutaneous fat layer adjacent to the 12th rib as well as the meat colour,was determined. The fatty acid composition of the longissimus muscle was changed byfeeding the rumen inert fat sources. The three predominant fatty acids found were palmitic,stearic and oleic acids. The palmitic acid (CI6:0) content of the muscle and diet was 24.44 &20.47,25.97 & 22.57,31.06 & 33.23, 30.98 & 37.91, 34.94 & 31.77 and 29.71 & 32.88 of thetotal fat for the LD, HD, LDm, HDm, LDgf and HDgf diets, respectively. The C16:0 contentwas significantly higher in the muscle of the calves receiving the LD diets supplemented withfat (P=0.0008). There was also a significant interaction between the two fat sources andprotein degradability (P=0.0065), but only in the LD diets. The stearic acid (CI8:0) contentof the muscle and diet was 14.35 & 5.22, 19.65 & 8.61, 17.29 & 4.68, 22.59 & 5.78, 22.27 &15.54, and 26.48 & 20.15 of the total fat for the LD, HD, LDm, HDm, LDgfand HDgfdiets,respectively. The C18:0 content was significantly higher in the muscle of calves receiving theHD (P=O.OOOl)compared to LD diets. The stearic acid content was also significantly higherwhen fat was added to LD (P=0.0042) or HD (P=0.0073) diets. The oleic acid (CI8:1)content of the muscle and diet was 36.06 & 21.51,39.99 & 21.11,32.21 & 23.67, 29.13 &24.59, 25.23 & 18.68 and 35.93 & 16.02 of the total fat for the LD, HD, LDm, HDm, LDgfand HDgf diets, respectively. The linolenic acid (CI8:3) content of the muscle wassignificantly higher (P=0.0038) when fat was added to LD diets compared to no fatsupplementation (0.87 vs. 0.15). The CIELAB values indicated that LD diets resulted in morepink meat. Mean values ofL* =-32.61, 34.19; a* = 7.08, 7.91 and b* = 3.18 and 4.07 wereobserved for the LD and HD diets, respectively. Meat from the LD diets had significantlylower L*-(P=0.0252), a*-(P=0.0283) and b*-(P=0.0109) values compared to meat from theHD diets. It was concluded that there was a positive response in CP digestibility when rumeninert fats were supplemented to LD or HD diets, although a greater response was shown in theLD diets. The FCR, dry matter and fat digestibility were only increased when fat was addedto the LD and not to the HD diets. Similarly, the fatty acid contents of the longissimusmuscle of veal calves can be manipulated with the supplementation of rumen inert fat sources,but only when combined with a low protein degradable diet. The low degradable protein dietsalso produce a more attractive meat colour for the potential veal consumer.

[发布机构] Stellenbosch University