The present study evaluated the interaction effects of omega-3 fatty acid (FA) (from linseed oil; LSO, 0 vs. 2.5, % DM basis) with rumen-undegradable to -degradable protein ratios [low ratio (LR) = 27:73; high ratio (HR) = 38:62 based on crude protein percent] in dairy calves’ starter diet. Forty-eight 3-d old female Holstein dairy calves (41.5 kg of BW) were allocated in a 2 × 2 factorial arrangements in the following treatments (n = 12 calves/each); (1) no supplementation of LSO with LR (NLSO-LR); (2) no supplementation of LSO with HR (NLSO-HR); (3) supplementation of LSO with LR (LSO-LR); and (4) supplementation of LSO with HR (LSO-HR). The calves weaned on d 53 of experiment and remained in the study until d 73. Intake was not affected by LSO and RUP: RDP ratio. However, average daily gain (ADG) was improved with LSO supplementation. Feeding HR diet increased ADG compared with LR diet during the entire period. Final body weight was greater in calves fed on LSO than those fed NLSO diet. Microbial protein production did not differ among treatments. Calves fed on LSO diets had greater feed efficiency than those which were not fed on LSO diets. The calves supplemented with LSO had greater wither and hip heights compared with the un-supplemented calves. The glucose, cholesterol, high density lipoprotein, and insulin concentrations increased in calves supplemented with LSO. In conclusion, the HR diet improved calf’s performance post-weaning; however, LSO could enhance growth performance of dairy calves during the pre-weaning period.
