Data and code from: Onset of feeding behavior in intensively housed dairy calves

Development of early feed and water intake is not well-documented in dairy
calves, and little is known about how traditional, intensive feeding
management influences the development of species-specific behaviors, like
rumination. Our first objective was to describe grain, water, and hay
intake in calves from birth. Our second objective was to evaluate whether
early access to hay influenced the likelihood of reaching biologically
relevant thresholds of grain and water intake (grain: 50, 100, 250, 500,
900 g; water: 1, 2, 3, 4, 5 L), and rumination (5, 10, 15, 20 % of a 24-h
d) compared to grain alone. Our third objective was to evaluate whether
hay provision affected the age at which calves reached these thresholds.
We enrolled 49 Holstein heifer calves over 2 yr (2018: 22; 2019: 27) that
were housed individually and fed milk replacer via a bottle (2018: 5.7-8.4
L/d; 2019: 3.8-5.6 L/d), as is common in the US. Calves received ad
libitum water and grain (Control: n = 20) with additional access to
chopped mountaingrass hay (Hay: n = 29) from d 0. Intake was measured
daily until the start of weaning at 49-51 d. Calves were ear-tagged at 3 ±
2 d (mean ± SD) of age with an accelerometer (SenseHub, Merck Animal
Health) that classified rumination by minute continuously through 38 ± 10
d (mean ± SD) of age. We analyzed age of onset as the first of 3
consecutive days that a calf met the threshold level with a zero-inflated
hurdle model. The logistic regression component of this model evaluated
whether access to hay affected the likelihood of reaching each onset
threshold. The second, conditional component of the model evaluated, among
the calves that met a given threshold, if having access to hay affected
the age they reached it. We found that calves consumed grain, hay, and
water within 1 d of birth. Calves consumed small quantities of hay
throughout the milk-fed period, typically < 100 g/d, but this still
led to differences in feeding development, with hay-fed calves reaching 5
% rumination at younger ages, and a greater proportion reaching higher
rumination thresholds compared to controls: specifically, 89 % vs. 53 %
reached the 15 % threshold, and 61% vs. 5 % reached the 20 % threshold
(Hay vs. Control, respectively). Hay-fed calves also tended to be more
likely to reach the 500 g grain threshold. There was no evidence that
access to hay affected age at reaching higher rumination or grain
thresholds, possibly because all calves were in similarly restrictive,
milk-limited environments, where calories from solid food intake were
particularly important. Calves with hay tended to reach the 3 L water
threshold at a younger age than controls, but there was no evidence that
hay affected likelihood of consuming increasing amounts of water. Overall,
our results demonstrate that calves will consume grain, hay, and water as
soon as they are provided, highlighting the importance of opportunities to
perform species-specific feeding behaviors. Withholding hay from very
young animals, which is common in the US and allowable under the EU 2008
Directive, limits the development of motivated behaviors like rumination.