An evaluation of skim milk powders subjected to different heating conditions during processing as dietary protein sources for the young pig

Abstract

The protein quality of 4 spray-dried skim milk powders which had been processed under different heating conditions and which had whey-protein nitrogen indices (W.P.N.I.) ranging from 1.24 to 6.94 mg g −1 powder was examined by measurements in vitro and by a metabolism study and 2 growth trials with 5-week-old pigs. Differences in the ability of the reconstituted milks to clot were found in vitro and in vivo with the higher W.P.N.I. powders forming a firmer clot more rapidly. The powders had similar fluorodinitrobenzene (F.D.N.B.)-available lysine levels with total lysine determined following acid hydrolysis (2.9 g per 100 g) being available. A small amount (24.3 mg per 100 g) of furosine was detected in each of the milk powders. In the metabolism study, 16 entire male pigs (10-kg liveweight) were given 4 semi-synthetic diets containing the respective milk powders as sole protein sources. Total collections of urine and faeces were made and contents of the terminal ileum were sampled following slaughter of the animals. In 2 growth trials each involving 24 pigs, 4 barley-based diets which each contained 1 of the 4 skim milk powders, supplying around one third of the dietary crude protein, were given ad libitum over the liveweight range 8–20 kg. There was no effect of diet on effect of diet on apparent faecal nitrogen digestibility ( X ̄ ± S.E. = 0.92±0.004 ), apparent ileal nitrogen digestibility ( X ̄ ± S.E. = 0.82±0.013 ) or apparent ileal amino-acid digestibility. Mean apparent ileal amino-acid digestibility ranged from 0.73 for serine to 0.96 for phenylalanine and tyrosine. Diet did not influence urinary metabolite excretions and a mean B.V. of 0.98 indicated that the absorbed protein was virtually completely utilized by the piglets. There was no significant effect of dietary treatment on growth performance in either trial. It was concluded that commercially-available spray-dried skim milk powders, although varying widely in W.P.N.I. are high-quality protein sources for young growing pigs.