Response to Incremental Replacement of Palm Oil with Fish Oil in Starter Diet on Growth Performance, Plasma Metabolites, Ruminal Fermentation, and Behavior of Dairy Calves

Simple Summary: In this study, we aimed to understand how different levels of fatty acids in the starter feed affect the growth and health of milk-fed calves. We divided 30 female calves into three groups and fed them starter feeds supplemented with different fatty acids: palm fatty acids (PO), a mix of palm fatty acids and fish oil (PFO), and fish oil (FO). We found that calves receiving FO had slightly greater body weight over the whole period compared to those receiving PFO or PO. However, overall growth rates and intake of feed remained similar across all groups. Additionally, parameters like body size, rumen fermentation, blood composition, and behavioral patterns were not affected by the type of fatty acids in their diet. Our study suggests that altering the ratio of different unsaturated fatty acids in starter feed may not have a substantial impact on the growth and metabolic performance of young calves under normal conditions. These findings contribute to our understanding of calf nutrition and may guide future strategies for optimizing their health and growth during the critical pre-weaning period. The objective of this study was to evaluate the effects of the incremental levels of n-3 fatty acids (FA) in starter feed (SF) on growth and metabolic performance of milk-fed calves. From day 3 of age, 30 female calves (39.4 +/- 3.1 kg of body weight) were randomly assigned to one of three dietary treatments: (1) SF supplemented with 3.3% palm fatty acids (PO), (2) SF supplemented with 1.7% of PO and 1.9% fish oil (PFO), or (3) SF supplemented with 3.9% fish oil (FO). Chopped straw (7.5% of DM) was included in the SF of all treatments as total mixed ration (TMR). Diets had similar energy and protein contents. Total n-3 FA (% of total FA) and n-6/n-3 of PO, PFO, and FO were 1.90, 6.80, and 11.8 and 15.5, 4.50, and 2.70, respectively. The BW was greater for calves receiving FO (60.2 +/- 0.3 kg) compared with PFO (58.7 +/- 0.3 kg; p = 0.007) and tended to be greater for calves receiving FO vs. PO (59.0 +/- 0.3 kg; p = 0.050). Because there was no interaction effect between diet x week of experiment, the greater BW of FO could not be attributed to the dietary treatment. Accordingly, average daily gain, total dry matter intake (DMI), starter DMI, and gain to intake ratio (G:FI) did not differ among dietary treatments during the entire period of the study (p > 0.05). Dietary treatments did not impact body size parameters such as body length, body girth, withers height, heart girth, hip height, and width (p > 0.05). Neither ruminal fermentation parameters nor blood variables were influenced by supplementing the types of oil at different time points. Calves' behavioral parameters, such as standing, lying, eating, and ruminating, were not influenced by different dietary treatments (p > 0.05). The number of days with abnormal fecal score was not different among dietary groups (p > 0.05). Overall, our findings suggest that changing the n-6/n-3 ratio in starter feed by incremental replacement of palm fatty acid with fish oil at a moderate supplemental level of similar to 3% of DM may not affect the growth and metabolic performance of young calves under non-challenged conditions.