Effects of feeding wheat straw or beet pulp in starters supplemented with either soybean oil or palm fatty acids on growth performance and urinary purine derivatives in dairy calves

The current study aimed to evaluate the effect of wheat straw (WS) as a forage fiber source vs beet pulp (BP) as a non-forage fiber source supplemented by fat sources soybean oil (SBO) vs palm fatty acid (PLF) on growth performance, protozoal population, and urinary purine derivatives (PD) in dairy calves. Fifty-two new-born Holstein female calves (3 days of age) were assigned randomly to one of four treatments: 1) starters contained WS with SBO (WS-SBO); 2) starters contained WS with PLF (WS-PLF); 3) starters contained BP with SBO (BP-SBO); and 4) starters contained BP with PLF (BP-PLF). An equal amounts of fiber (75 g/kg dry matter) and fat (25 g/kg dry matter) was offered in experimental treatments. Milk feeding schedule was constant among experimental treatments. The starter intake was higher in calves received BP with PLF diet (P = 0.02) compared to calved received SBO diet. This coincided with fiber x fat source interaction (P = 0.05) for average daily gain (ADG) and hence BW was higher in calves fed BP along with PLF (P = 0.04). The heights for withers (P = 0.04) and hips (P = 0.01) were higher at weaning when calves received BP with PLF compared to SBO diets. Moreover, the higher ruminal concentration for short-chain fatty acids (P = 0.05) and the higher digestibility for organic matter (P = 0.03) and neutral detergent fiber (P = 0.05) were ach-ieved when calves fed BP with PLF compared to SBO diets. Supplemental SBO reduced starter intake (P = 0.04), total dry matter intake (P = 0.01) and ADG (P = 0.01) compared to PLF diet. The protozoa population was reduced (P = 0.01) when calves were supplemented with SBO compared to calves fed PLF. Furthermore, supplemental SBO reduced total PD concentrations (P = 0.02) and conse-quently reduced microbial protein synthesis (P = 0.02) compared to PLF diets. Feeding BP compared to WS reduced acetate to propionate ratio (P = 0.02) during the pre-weaning period. In conclusion, based on the current study conditions, feeding WS compared to BP did not produce large differences, because of the negative results produced by SBO compared to PLF on both rumen fermentation and nutrient digestibility, feeding SBO is not advisable, whereas feeding PLF in conjunction with BP appears to provide a significant boost in growth and feed consumption in young dairy calves.