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

Thesis (MSc)--Stellenbosch University, 2000.

ENGLISH ABSTRACT: Six groups each with six Friesian bull calves were used in this investigation and slaughtered at 20 weeks of age. Calves received a low- (LD) or high (HD) degradable protein diet, each with 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. The starter diets were fed ad lib. from day 14 to 10 weeks of age and finishing diets ad lib. from 11 to 20 weeks of age. There were no significant differences in body mass gain or dry matter intake over the entire 20 week period. The feed conversion ratio (FCR) was improved significantly (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, using chromium oxide (Cr203) as a marker, during week 18 of the investigation. Digestibility values (%) 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 crude protein 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 was added to LD diets. The crude protein (CP) digestibilities were significantly higher when fat was 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 by feeding 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 the total fat for the LD, HD, LDm, HDm, LDgf and HDgf diets, respectively. The C16:0 content was significantly higher in the muscle of the calves receiving the LD diets supplemented with fat (P=0.0008). There was also a significant interaction between the two fat sources and protein degradability (P=0.0065), but only in the LD diets. The stearic acid (CI8:0) content of 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 the HD (P=O.OOOl)compared to LD diets. The stearic acid content was also significantly higher when 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, LDgf and HDgf diets, respectively. The linolenic acid (CI8:3) content of the muscle was significantly higher (P=0.0038) when fat was added to LD diets compared to no fat supplementation (0.87 vs. 0.15). The CIELAB values indicated that LD diets resulted in more pink meat. Mean values ofL* =-32.61, 34.19; a* = 7.08, 7.91 and b* = 3.18 and 4.07 were observed for the LD and HD diets, respectively. Meat from the LD diets had significantly lower L*-(P=0.0252), a*-(P=0.0283) and b*-(P=0.0109) values compared to meat from the HD diets. It was concluded that there was a positive response in CP digestibility when rumen inert fats were supplemented to LD or HD diets, although a greater response was shown in the LD diets. The FCR, dry matter and fat digestibility were only increased when fat was added to the LD and not to the HD diets. Similarly, the fatty acid contents of the longissimus muscle 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 diets also produce a more attractive meat colour for the potential veal consumer.

AFRIKAANSE OPSOMMING: Ses behandelings, lae- (LD) of hoë (HD) degradeerbare diëte, elk met of sonder rumeninerte vetsupplementering, is geëvalueer met ses kalwers in elke groep. Twee kommersiële vetbronne is gebruik, nl. Morlae (m) en Golden Flake (gf) teen 'n 2.5% insluitingspeil. 'n Kommersiële melksurrogaat (Denkavit) is aangebied teen 4L1dag tot 42 dae ouderdom, gevolg deur 2L/dag tot speenouderdom op 49 dae. Aanvangsdiëte is ad lib. aangebied vanaf 14 dae tot 10 weke ouderdom en die groeidiëte ad lib. vanafweek 11 tot 20. Daar was geen betekenisvolle verskille in die totale massatoename of die droëmateriaalinname nie. Die voeromsettingsverhouding is betekenisvol verbeter (P=0.0032) in die behandelings waarin rumeninerte vette by LD diëte ingesluit is, maar nie by die HD diëte nie. Die voeromsettingsverhouding (kg droëmateriaalinname / kg massatoename) van die LD, HD, LDm, HDm, LDgf en HDgf diëte was 3.45, 3.44, 3.07, 3.81, 3.02 en 3.43, onderskeidelik. Al 36 kalwers is in 'n verteringsproef gebruik gedurende week 18 van die proef. Chroomoksied (Cr203) is as merker gebruik. Verteerbaarheidswaardes vir die ses diëte was 61.74, 65.91, 75.44,69.00,75.54 en 67.15 vir droëmateriaal, 61.44, 61.60, 71.33, 68.23, 75.44 en 66.12 vir ruproteïen en 58.56, 66.45, 75.98, 70.92, 78.43 en 70.79 vir vet, onderskeilik. Die droëmateriaal- (P=O.OOOl) en vetverteerbaarheid (P=O.OOOI) was slegs betekenisvol hoër wanneer vet by LD diëte gevoeg is en nie by HD nie. Die ruproteïen (RP) verteerbaarheid Stellenbosch University http://scholar.sun.ac.za VI was betekenisvol hoër (P=0.0002) by LD en HD (P=0.0488) diëte met vet supplementering, teenoor geen vet insluiting. Die kalwers is op 20 weke ouderdom geslag en die vetsuursamestelling van die vleis (m. longissimus) en die subkutane vetlaag teenaan die 12de rib, asook en die vleiskleur, is bepaal. Die vetsuursamestelling van die longissimus spier is deur die supplementering van rumeninerte vet verander. Die drie primêre vetsure wat in die vleis voorgekom het, was palmitiensuur, steariensuur en oleïensuur. Die palmitensuur (CI6:0) inhoud van die spier en diëte was 24.44 & 20.47, 25.97 & 22.57, 31.06 & 33.23, 30.98 & 37.91, 34.94 & 31.77 en 29.71 & 32.88 van die totale vet van die LD, HD, LDm, HDm, LDgf en HDgf diëte, onderskeilik. Die C16:0 was betekinisvol hoër in die spiere van kalwers wat die LD diëte met vet supplementering (P=0.0008) ontvang het. Die steariensuur (CI8:0) inhoud van die spier en diëte was 14.35 & 5.22, 19.65 & 8.61, 17.29 & 4.68, 22.59 & 5.78, 22.27 & 15.54, en 26.48 & 20.15 van die totale vet vir die LD, HD, LDm, HDm, LDgf en HDgf diëte, onderskeidelik. Die C18:0 inhoud was betekinisvol hoër in die spiere van die kalwers wat die HD (P=O.OOOI),teenoor LD diëte ontvang het. Die steariensuur inhoud was ook betekenisvol hoër wanneer vet by LD (P=0.0042) of HD (P=0.0031) diëte gevoeg word. Die oleïensuur (CI8:1) inhoud van die spier en diëte was 36.06 & 21.51, 39.99 & 21.11, 32.21 & 23.67, 29.13 & 24.59, 25.23 & 18.68 en 35.93 & 16.02 van die totale vet vir die LD, HD, LDm, HDm, LDgf en HDgf diëte, onderskeidelik. Die linoleensuur (CI8:3) inhoud van die spier was betekinisvol hoër (P=0.0038) in die LD diëte met vet teenoor LD met geen vet supplementering (0.87 vs. 0.15). Die CIELAB waardes van die LD diëte dui op 'n pienker vleiskleur. Gemiddelde waardes van L* = 32.61 & 34.19, a* = 7.08 & 7.91 en b* = 3.18 & 4.07 is vir die LD en HD diëte, onderskeidelik, waargeneem. Die vleis van die LD diëte het 'n betekenisvol laer L*-(P=0.0252), a*-(P=0.0283) en b*-(P=0.0109) waarde in vergelyking met die HD diëte getoon. Die resultate dui daarop dat daar 'n positiewe respons in die ruproteïenverteerbaarheid by die supplementering van rumeninerte vette by LD en HD diëte voorkom, maar die response op die LD diëte is groter. Die voeromsettingsverhouding, droëmateriaal- en vetverteerbaarheid is egter net bevoordeel in die LD met vet en nie in die HD diëte nie. Die vetsuursamestelling van die longissimus spier in die kalf kan gemanipuleer word met die supplementering van rumeninerte vetbronne, maar slegs wanneer dit gekombineer word met lae degradeerbare proteïen diëte. Die lae degradeerbare proteïen diëte produseer ook die mees aanloklike vleiskleur vir die potensiële kalfsvleisverbruiker.

Masters