Soybean oil supplementation and starter protein content: Effects on growth performance, digestibility, ruminal fermentation, and urinary purine derivatives of Holstein dairy calves

摘要

This study investigated the effects of feeding dairycalves starter diets containing 19% or 22% crude protein(CP) content on a dry matter basis and eithersupplemented or not with soybean oil (SBO, 0 vs. 3%,dry matter basis) on growth performance, digestibility,urinary nitrogen, and purine derivatives (PD) excretion.A total of 48 female Holstein dairy calves (mean39.8 kg of body weight) were randomly distributed toexperimental diets in a 2 × 2 factorial arrangement oftreatments. The 4 dietary treatments were (1) starterdiet without SBO supplement and 19% CP (NSBO-19CP), (2) starter diet without SBO supplement and22% CP (NSBO-22CP), (3) starter diet with 3% SBOand 19% CP (SBO-19CP), and (4) starter diet with3% SBO and 22% CP (SBO-22CP). Milk feeding valuewas similarly based on a constant protocol across experimentaltreatments and calves had ad libitum accessto water and starter diets throughout the study. Allcalves were weaned on d 63 of age and remained inthe study until d 83 of age. Calves supplemented withSBO had lower starter feed intake and average dailygain (ADG) and lower feed efficiency (FE) but hada higher fecal score indicating a higher likelihood ofdiarrhea occurrence compared with unsupplementedcalves. Wither heights, digestibilities of organic matter,CP, and neutral detergent fiber were decreased, andruminal volatile fatty acids tended to be reduced, andthe molar proportion of ruminal butyrate (preweaning)and acetate (postweaning) reduced by supplementalSBO. The urinary allantoin and total PD excretionwere reduced; however, urinary nitrogen excretion wasincreased when calves were supplemented with SBO.The CP amount did not affect starter feed intake, FE,or diarrhea occurrence rate, whereas the 22CP dietsincreased neutral detergent fiber digestibility, improvedADG (tendency), and increased allantoin and urinaryPD excretion compared with the 19CP diets. Thestarter feed intake, ADG, FE, diarrhea occurrencerate, nutrient digestibility, and ruminal fermentationwere not affected by the interaction between starterSBO and CP level; however, hip height and total PDin calves that received the SBO-22CP diets were higherthan those fed the SBO-19CP diets. In conclusion,based on our experimental conditions, supplementalSBO could not be recommended for dairy calves. Furthermore,our findings indicate that SBO has negativeeffects on performance more attributed to reducingstarter intake, digestibility, and ruminal volatile fattyacid concentration rather than because of a limitationof starter metabolizable protein supply and intestinalamino acid availability. Therefore, our results indicatethat feeding the higher starter CP content is not a viablestrategy to compensate for the negative effects ofSBO supplementation on the growth performance ofdairy calves.