The role of solid feed amount and composition and of milk replacer supply in veal calf welfare

Abstract

Diets used in veal production were linked with welfare problems: that is, behavioral and gastrointestinal health disorders. This study aimed to determine how indicators of calf welfare, that is, behavior and some characteristics of the feces reflecting gastrointestinal health status, are affected by (1) different amounts and compositions of solid feed (SF), (2) the addition of ad libitum long straw to a typical veal diet, and (3) milk replacer (MR) being fed via automated milk dispensers (AMD). Two-week-old Holstein-Friesian bull calves (n=270) were used in this study. In a 4×2 factorial design, 32 pens (5 calves per pen) were allocated to different levels of SF (SF1, SF2, SF3, or SF4) and roughage-to-concentrate ratios (20:80 or 50:50). The experimental period (13 to 29wk of age) was preceded by an adaptation period (3 to 12wk of age). Targeted total dry matter (DM) intake from SF during the experimental period was 20 kg of DM for SF1, 100 kg of DM for SF2, 180 kg of DM for SF3, and 260 kg of DM for SF4. The roughage part of the SF was 50% maize silage and 50% chopped wheat straw (on a DM basis). Ten additional pens were allocated to 2 treatments with ad libitum SF, with either (1) SF components in separate troughs (SEP) or (2) SF components mixed, with the composition being equal to the choice of SEP calves in the preceding week (MIX). Another 4 pens were fitted with racks filled with long wheat straw (STR) and fed SF2 with a roughage-to-concentrate ratio of 20:80. All the aforementioned pens received MR in buckets. Finally, 8 pens were allocated to 1 of 2 SF levels: SF1 or SF2 (with a roughage-to-concentrate ratio of 50:50) and fed MR via an AMD. Milk replacer provision was adjusted every 2wk to achieve similar rates of carcass gain across treatments (excluding SEP, MIX, and STR). Behavior was recorded at 15 and 24wk using instantaneous scan sampling. The prevalence of diarrhea and clay-like feces, which signal ruminal drinking, was monitored at 14 and 25wk. More roughage, but not concentrate, increased rumination and decreased tongue playing. The STR calves had higher rumination and lower abnormal behavior levels compared with calves without ad libitum straw. Offering MR via an AMD reduced tongue playing at 15wk. Tongue playing frequency was related to both roughage amount and AMD feeding, suggesting 2 separate motivations (i.e., rumination and sucking) underlying the development of this behavior. Only SF amount affected aspects of feces: SF1 calves had the highest diarrhea incidence. No effect of diet was found on clay-like feces.

Keywords: behavior; milk feeding method; roughage-to-concentrate ratio; solid feed level; veal calf.