Effect of tomato pomace and different ratios of linoleic acid to alpha-linolenic acid in starter diet on growth performance and blood metabolites in Holstein calves

The present study aimed to investigate the effect of using tomato pomace (TP) in the starter feed containing different ratios of linoleic acid to alpha-linolenic acid by including pure fat powder or calcium salt of flaxseed oil (FO) on growth performance and blood metabolites in calves before and after weaning. For this purpose, 48 7-day-old Holstein calves were allocated to 1 of 4 treatments in a 2 × 2 factorial arrangement: starter feed without TP and FO (NTP-NFO; ratio of C18:2 to C18:3 = 12.39), starter feed containing 25 g/kg calcium salt of FO without TP (NTP-FO; ratio of C18:2 to C18:3 = 2.54), starter feed containing 100 g/kg TP without FO (TP-NFO; ratio of C18:2 to C18:3 = 12.21), and starter feed containing 25 g/kg calcium salt of FO and 100 g/kg TP (TP-FO; ratio of C18:2 to C18:3 = 2.48). All calves were weaned gradually from d 51–56 and remained in the trial until d 70 of the study. Results showed that TP × FO interaction was observed for several traits, whereby FO increased days in diarrhea, fecal score, and superoxide dismutase concentration and decreased insulin concentration when diet had not TP, but had the opposite effect when diets had TP. Furthermore, FO supplementation decreased starter feed intake in NTP diets and increased it in TP diets. The TP had no significant effects on final body weight (BW) and feed efficiency; however, TP-fed calves tended to have greater white blood cells and had greater neutrophil and lower low dencity lipoprotein (LDL) concentrations than NTP-fed calves. Moreover, calves fed starter feed containing TP had greater ruminal butyrate concentration than NTP-fed calves. Calves that received FO treatments had lower BW and starter feed intake and tended to have lower average daily gain (ADG) than those that did not receive FO. Regardless of TP, feeding FO increased eosinophils and decreased malondialdehyde compared with unsupplemented calves. Overall, our results showed that supplementation of starter feed with 100 g/kg TP adversely affected calves' performance. Also, adding 25 g/kg of FO in starter feed decreased calves' BW and starter feed intake, indicating that dietary FO may be less effective at improving performance during the early months of life. Calves fed TP-FO treatment had better performance than calves fed TP or FO alone, which indicates the synergic effect between TP and FO on the performance and health of dairy calves. • Usage of 10% of tomato pomace had no adverse effect on calves' performance. • Adding 2.5% of flaxseed oil decreased calves' BW and increased fecal score. • Tomato pomace and flaxseed oil had synergic effect on calves’ performance.