The utilization of milk diets with different fat content by the preruminant calf 1. Digestibility and metabolizability of the diets and live mass gain of the calves

Abstract

Agt-en-twintig Friesbulkalwers is op vier dae ouderdom by vier groepe ingedeel en tot die ouderdom van 21 dae in metabolismekratte gevoer
op melkdiete wat van 147g tot 444g bottervet per kalf per dag voorsien het. Hoewel volume-innames met slegs 18 %verhoog is vanaf die laagste tot die hoogste voedingspeil, het ME-innames meer as verdubbel vanaf 10,6 MJ tot 21,6 MJ. Die gemiddelde daaglikse N- innames het toegeneem vanaf 19,6 g (A) tot 20,7 g (D) per kalf terwyl proteiten:energie verhoudings verander het van 1 : 90 (A) tot 1 : 168 (D). Die metaboliseerbaarheid van die energie in die vier diete was, onderskeidelik, 93,0 ±2,2; 94,2 ±3,1; 93,3 ±3,2 en 91,8 ±4,0 en die balansproefresultate het getoon dat die skynbare verteerbaarheid van vet verlaag is in die twee diete met hoogste vetkonsentrasie. Dit het gepaard gegaan met 'n meer algemene voorkoms van buikloop onder kalwers in hierdie twee Groepe C en D. Energie- enstikstofverliese deur die urine het afgeneem
namate energie-innames gestyg het, 'n Verhoogde doeltreffendheid van proteienbenutting is aangetoon deur die stygende gemiddelde stikstofretensies,
maar daar was 'n duidelike afplatting by die hoogste energiepeil op te merk. Die retensie van skynbaar verteerde proteiten het gesfyg vanaf 65,9% by Groep A tot 76,3 %by Groep C. Gemiddelde lewende massa toenames van 314 ±67,414 ±48,557 ±78 en 567 ± 133 g per kalf per dag is by die vier groepe onderskeidelik, vasgestel. Die positiewe verwantskap tussen lewende massa toenames (Y) en ME-innames (X) kon beskryf word met die vergelyking Y = 1,7747X - 18,9478 r = 0,8447.

Twenty-eight Friesland bull calves, four days of age, were allotted to four groups and were offered milk diets which supplied 147 g to 444 g butterfat per calf per day for 21 days. Mean daily ME intakes increased from 10,6 MJ to 21,6 MJ while volume intakes differed by only 18% from the lowest to the highest feeding level. Mean daily nitrogen intakes increased from 19,6 g (A) to 20,7 g (D) per calf while protein: energy ratios were widened from 1:90 to 1:168. Metabolizability of GE were 93,0±2,2; 94,2±3,1; 93±3,2 and 91,8±4,0 in the four diets respectively and it was shown that apparent digestibility of fat was depressed on the two highest fat diets, mainly as a result of scouring which occurred with higher incidence in Groups C and D. Urinary energy- and urinary nitrogen losses decreased as energy intakes increased. A better utilization of dietary protein, at the higher levels of energy intake, was shown by an increased nitrogen retention by calves on the higher energy diets, although there was a levelling-off at the highest energy intake. Retention of apparently digested nitrogen increased from 65,9% in Group A to 76,3% in Group C. Mean live mass gains of 314 ±67, 414 ±48,557 ±78 and 567 ±133 g per calf per day were recorded in the
four groups respectively. The highly significant regression equation describing the relationship between live mass gain (Y) and ME-intake (X) was Y=1,7747X - 19,9478. r = 0,8447.