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Transitioning weaned dairy calves to TMR may affect growth

July 2, 2020


Tim Lundeenn



Calves converted to TMR as early as eight weeks still achieved adequate growth. The weaning transition period for dairy calves has been a common research focus, particularly for the Heinrichs lab at Penn State University. The group recently published a study on converting weaned dairy calves from a component-fed ration to a total mixed ration (TMR) at eight, 10 or 12 weeks of age for the effect on intake, growth and nutrient digestibility.

L.K. Mitchell, C.M. Jones and A.J. Heinrichs with Penn State University randomly assigned 40 Holstein calves to one of four groups: no TMR or TMR conversion at eight, 10 or 12 weeks — T0, T8, T10 and T12, respectively. Calves were weaned at six weeks of age, housed individually and studied from seven to 14 weeks of age. Mitchell et al. noted that rations, which consisting of a 20% crude protein texturized starter and grass hay, were offered ad libitum as separate components or as a TMR with 85% starter and 15% grass hay on a dry matter basis.

Intakes and bodyweights were measured weekly, the researchers said, and the component intake for TMR was calculated from the proportion of grass hay and starter contained in the TMR.

Fecal grab samples were collected every nine hours over three days for a total of eight samples that formed a composite at nine, 11 and 13 weeks of age from the same four calves per group. Rumen fluid samples were collected via esophageal tube at negative one, zero, three and seven days relative to conversion from component to TMR, Mitchell et al. said.

According to the researchers, average daily gain and final bodyweights tended to be least for calves on the T8 treatment. Mitchell et al. said empty bodyweight gain was significantly less for T8 calves than for T0 calves but did not differ from either the T10 or T12 calves: T0 = 1.07 kg, T8 = 0.93 kg, T10 = 1.02 kg and T12 = 1.04 kg per day. Furthermore, the researchers said hip growth tended to be least for T8 calves, which resulted in lower final hip width: T0 = 25.9 cm, T8 = 25.2 cm, T10 = 25.6 cm and T12 = 25.8 cm.

According to the researchers, intake tended to be reduced for calves converted earlier to the TMR, and throughout the study, calves fed TMR ate more hay and less starter than component-fed calves.

Mitchell et al. reported that metabolizable energy intake was less for T8 calves versus T0 calves but did not differ from the T10 or T12 groups: T0 = 8.46 Mcal, T8 = 7.55 Mcal, T10 = 8.01 Mcal and T12 = 8.23 Mcal per day.

They said no differences were observed in feed efficiency for the duration of the study. Also, differences in dry matter digestibility were not observed, but fiber digestibility was greater for calves fed TMR at nine, 11 and 13 weeks of age, Mitchell et al. reported, adding that conversion to TMR increased rumen pH.

The researchers concluded that TMR conversion increased hay consumption and subsequently decreased starter and total dry matter intake, which led to reduced weight and structural growth. However, they said calves that were converted to TMR as early as eight weeks still achieved adequate growth.

The increase in rumen pH and subsequent increase in fiber digestibility allowed for calves to be converted to a 15% grass hay TMR as early as eight weeks and still achieve desirable growth goals, according to Mitchell et al.


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