Invited review: The effect of milk feeding practices on dairy calf behavior, health, and performance-A systematic review

Invited review: The effect of weaning practices on dairy calf performance, behavior, and health-A systematic review

The aim of this systematic review was to summarize the literature assessing the effects of weaning practices on performance, behavior, and health of dairy calves. Only published, peer-reviewed articles written in English and specifically assessing the effects of weaning treatments on dairy calves were eligible for inclusion. Studies had to include 2 or more treatment groups that addressed at least one of 4 interventions: weaning age (i.e., when milk was fully removed), weaning duration (i.e., number of days from start of milk reduction to when milk was fully removed), weaning criteria (e.g., age vs. intake), or alternative weaning methods (e.g., water dilution). Outcome measures could include starter intake, growth (BW or ADG), behaviors (5 specific sucking behaviors; play behavior; lying behavior; vocalizations; unrewarded visits to an automated milk feeder), and health (mortality rate, diarrhea, and respiratory illness). We conducted 3 targeted searches using Web of Science and PubMed. The articles underwent a 2-step screening process, resulting in a final sample of 44 studies. The majority of studies investigated weaning age (n = 22), followed by weaning duration (n = 13), weaning criteria (n = 9), and other weaning methods such as dilution, linear versus step-down milk reduction, or meal-based approaches (n = 6). There was consensus for positive effects (or at least no negative effects) on overall growth of calves weaned at later ages, over longer durations, based on starter intake, or weaned using step-down or meal-based milk removal approaches. This is despite reduced starter intake in calves weaned at later ages; most studies found improved starter intake in calves weaned over longer durations. Weaning based on starter intake had superior growth and feed intakes compared with calves weaned at a fixed earlier age. Few studies assessed interactive effects of weaning method and milk allowance. However, weaning after 8 wk appears to support superior weight gain, provided preweaning milk allowances are adequate (above 6 L/d). Weaning can lead to hunger-related behaviors and reduced welfare, yet only half of the studies assessed the effects of weaning method on calf behavior. Weaning at later ages can reduce signs of hunger (based on unrewarded visits to the milk feeder), but it is unclear if weaning over longer durations or weaning by starter intake reduces or prolongs hunger. There was little consensus among the few studies that measured oral behaviors of calves. Positive welfare indicators, such as play behavior, were rarely measured, yet are crucial to understanding the emotional states of calves during this potentially stressful diet transition. Health was rarely the primary objective of the study, with low sample sizes to conduct statistical comparisons. Overall, there remains significant knowledge gaps in our understanding of how best to wean calves. A successful weaning program must minimize signs of hunger while promoting high growth and feed intakes, so we encourage future work to include behavioral indicators of hunger and positive welfare to evaluate how weaning methods are experienced by the calf.

Using the conditioned place preference paradigm to assess hunger in dairy calves: Preliminary results and methodological issues

Dairy calves are typically fed restricted amounts of milk. Although feed restrictions are predicted to result in negative affective states, the relative aversiveness of 'hunger' remains largely unexplored in this species. Here, we investigated whether the conditioned place preference paradigm can be used to explore how calves feel when experiencing different levels of satiation. This paradigm provides insight into what animals remember from past experiences, the assumption being that individuals will prefer places associated with more pleasant or less unpleasant experiences. Sixteen Holstein calves were either fed a restricted (3 L per meal totalling 6 L per day) or 'enhanced' milk allowance (ad libitum up to 6 L per meal totalling up to 12 L per day) in their home-pen. Calves were then placed in a conditioning pen for 4 h immediately after being fed their morning meal to allow them to develop an association between the pen and their state of post-prandial satiation. Calves were conditioned across four days with their satiation state alternating between days to allow them to develop an association between pen and satiation levels. On the 5th day, calves were individually allowed to roam freely between the two pens for 30 min. We expected that calves would prefer the pen where they previously experienced higher levels of satiation, but our results show no to limited effects of treatment. However, some methodological issues (colour and side bias) prevent us from drawing strong conclusions. We discuss reasons for these issues and potential solutions to avoid these in future studies.

Effect of feeding calf starter with calcium salts of medium-chain fatty acids on the growth and metabolic hormones in calves

We investigated the effects of a calf starter supplemented with calcium salts of medium-chain fatty acids (MCFA-Ca) on growth and plasma hormone concentration in calves. Twelve Holstein calves were randomly assigned to two dietary groups (without supplementation [CON] and supplemented with MCFA-Ca [MCFA]) from 4 d of age. Calves were fed 1.0 kg/d of milk replacer until 5 wk of age and were completely weaned at 7 wk of age. Calves in the MCFA group received a calf starter containing 1% MCFA-Ca. dry matter intake (DMI) was measured daily, and body weight was measured weekly. Rumen fluid was collected at 13 wk of age to measure pH and volatile fatty acid concentration. Preprandial blood samples were collected weekly to measure the basal plasma hormone and metabolite concentrations. At 4, 8, and 13 wk of age, peri-prandial blood samples were collected every 30 min, from 60 min before feeding to 120 min after feeding, to observe metabolic responses to feeding. In addition, insulin sensitivity was assessed using euglycemic-hyperinsulinemic clamps at 4, 8, and 13 wk of age in three calves from each treatment. There were no differences in starter and hay DMI between the treatments. However, the average daily gain (ADG) after weaning was higher in the MCFA group than in the CON group. Weekly changes in plasma parameters did not differ between the treatments. Plasma concentrations of preprandial ghrelin and postprandial total ketone bodies at 13 wk of age were higher in the MCFA group than in the CON group. At 8 wk of age, peri-prandial plasma insulin concentrations were lower in the MCFA group than in the CON group. There were no differences between the treatments in terms of insulin sensitivity. The present study suggested that feeding weaning calves MCFA-Ca increases the ADG during the postweaning period, which may be mediated by endocrine signals, such as enhanced ghrelin secretion and decreased insulin secretion, without altering insulin sensitivity.