Necro-hemorrhagic enteritis in calves, caused by Clostridium perfringens type A, is a fatal disease, mostly affecting calves in intensive rearing systems. The lack of development of active immunity against α toxin, an essential virulence factor in the pathogenesis, has been proposed as a main trigger. In this experimental study, the effect of a set of milk replacer components on α toxin production, and the effect of lactose on in vivo antibody production, were investigated. For the latter, Holstein-Friesian bull calves (n = 18) were fed an all liquid diet that contained either a milk replacer with high-lactose content (45% DM) or the same milk replacer that was lactase treated, resulting in a lactose-free equivalent. Antibody levels against α toxin were monitored from 2 to 12 wk of age. In the in vitro part of the study, a concentration-dependent inhibitory effect of lactose on in vitro C. perfringens α toxin activity was observed, whereas protein did not influence α toxin activity. The in vivo experiment then showed from the age of 10 wk onwards, that anti-α toxin antibody levels of high-lactose animals declined, whereas antibody levels of the animals consuming lactose-free milk replacer remained the same throughout the trial. This points to a natural decline in maternal immunity of lactose-consuming animals, that is not compensated by the development of an active immunity, resulting in inferior protection. This study suggests that dietary lactose reduces C. perfringens α toxin production in vivo, which may lead to a decreased antigen presentation and thus lower serum antibody levels against the toxin. Consequently, any event causing massive α toxin production puts lactose-consuming calves at higher risk of developing necro-hemorrhagic enteritis.

The consumption of forages high in slow-degradable carbohydrates by dairy cattle leads to greater ruminal acetate production, which benefits milk fat content. Although tropical grasses are typically rich in fibrous materials, the milk fat content of dairy cows in Southeast Asia is low. Here, we investigate the effects of the species and harvest time of three common tropical grasses (Guinea, King, and Mulato II) harvested at three instances (early, normal, late) on in sacco degradation kinetics and in vitro gas production (IVGP) characteristics. Grass samples were subjected to (1) chemical analysis, (2) a fully automated in vitro gas recording system using rumen fluid to measure fermentation characteristics over 72 h, and (3) in sacco degradation using the nylon bag technique, employing seven incubation times up to 336 h. Forage quality decreased with maturity, as reflected in changes to digestibility and fiber content. Overall, early harvested grasses yielded the highest total gas production (311 ± 12.5 mL/g OM) followed by normal (300 ± 45.7 mL/g OM) and late (273 ± 19.5 mL/g OM) harvested grasses. The in vitro fermentable fraction (A1 + A2) was the highest for early harvested grasses, with the A2 parameter, relevant for milk fat content, being the highest for Guinea (81.6% A2/(A1 + A2)) and the lowest for King grass (71.0% A2/(A1 + A2)). Consequently, early harvested Guinea had the longest incubation times (10.5 h) and lowest fermentation rates (Rmax2 = 12.8 mL/g OM/h). Regression analysis showed relationships between NDF content and degradability. Harvesting tropical grass earlier than customarily practiced enhanced forage quality and ruminal degradability. Of the three grasses studied, each at three levels of maturity, early harvested Guinea grass was the most promising candidate for improving milk fat content in Southeast Asian dairy cows. This grass showed a high fermentable OM content, with a large proportion of slow-degradable carbohydrates.

Necrohemorrhagic enteritis (NHE), caused by Clostridium perfringens, predominantly affects white veal calves and usually has a fatal outcome. The C. perfringens α toxin is essential for lesion development, and as such, antibodies against this toxin are potentially protective. In the present prospective cohort study, we aimed to describe the seroepidemiology of C. perfringens α toxin under commercial veal calf rearing conditions to characterize the dynamics of the humoral immune response. Furthermore, we investigated the association between α toxin antibody development and carcass weight under the farming conditions for white veal calf production. From 2 to 24 wk of age, 40 male Holstein-Friesian calves were housed and reared under commercial veal calf conditions, receiving milk replacer and solid feed. Serum and fecal samples were collected at 4, 10, 12, 14, 18, 20, and 24 wk of age, and animals were weighed every 2 wk, up until 10 wk. At the end of the production period, animals were slaughtered and hot carcass weight (HCW) was determined. Antibody levels against C. perfringens α toxin were monitored over time. Upon arrival, 97.4% of the calves was seropositive. Antibody levels gradually declined, and a gap was observed between 14 and 20 wk of age, with an estimated nadir at 17.3 wk. Average daily gain was numerically higher for seropositive animals (0.95 ± 0.11 kg/d) than seronegative animals 0.85 ± 0.16 kg/d), resulting in a clear difference in HCW between calves that were seronegative and seropositive at the end of the study, as the latter weighed 13.4 kg more. Our data identified the critical window of maximum susceptibility to α toxin, potentially explaining why NHE-associated sudden death frequently manifests in calves aged 16 to 20 wk. The positive association between α toxin seropositivity and HCW suggests increased exposure to α toxin with solid feed intake. Taken together, the present study provides information relevant for the design of preventive strategies against NHE in terms of vaccination or nutritional management.