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3 critical periods in a calf’s life: The third

A. F. Kertz for Progressive Dairy Published on 12 May 2020

The three critical periods in a calf’s life are around calving, which includes the cow and colostrum management, the first two weeks of life when most deaths occur, and the two weeks before and after weaning. The first two critical periods have been addressed in a previous article, 3 critical periods in a calf’s life: The first and second.

Since a calf is a non-functioning ruminant when it is born, the milk or milk replacer goes into the abomasum (true stomach) and bypasses the rumen. As dry calf starter is eaten, it empties into and leads to the functional development of the rumen. In the meantime, the liquid diet meets nutrient needs for maintenance and growth, primarily in terms of energy and protein. Transition to dry diet needs to occur, and this requires functional development of the rumen. Dependent on the amount of milk or milk replacer fed, and its energy and protein levels, this will determine how much protein and energy is available for daily gain. The weaning transition period, two weeks before and two weeks after full weaning, determines how well calves perform at that time and in the future.




Water is the most essential nutrient needed in the greatest quantity for calves. In fact, the calf’s body is 70% water. When calves scour (diarrhea) they drink more water (drinking water does not cause scours) it is a compensation by the calf due to loss of body water, and it is directly related to dry matter intake (DMI) – limit it and you limit DMI and performance. Water intake should be 4 times dry matter intake, and good managers achieving good results figure out how to feed water. In cold weather, feed warm water, as that will reduce the calf’s energy needs to warm the cold water.

Liquid and starter feeding program

A transition to a dry diet needs to occur, and this requires functional development of the rumen. If done properly, this leads to calves being in good shape to enter their first grouping. It is important that feeding and management changes be done with transitions, as the calf is the most vulnerable animal to change on a dairy. The amount of milk or milk replacer fed, and its energy and protein levels, will determine how much protein and energy is available for daily gain. This is illustrated in Figure 1, along with typical calf starter intakes and their impact on daily gain.

043020 kertz fg 1

As starter intake averages 1 pound or more  per day (first of the four-week weaning transition period), one of the two daily feedings of milk or milk replacer can be eliminated. Starter intake should then double (2 pounds) from the previous week (second of four weeks), allowing full weaning the following week (third of four weeks) when starter intake would again double from the previous week to 4 or more pounds per day. This third week, and the following week (fourth of four weeks), daily gain should average 1.8 to 2.0 pounds – the rate of daily gain that should be maintained for the next 22 months, until that heifer has her first calf at about 24 months of age, weighing about 1,400 pounds before calving. The accepted goal of the Dairy Calf and Heifer Association is to double a calf’s birthweight at 2 months of age. In Figure 1, calves fed the 28% protein/15% fat milk replacer did that. There are various combinations of milk, milk replacer and starter feeding programs which can achieve that goal.

Rumen development

The key to rumen development is to feed a good texturized starter and to not feed hay until after 2 months of age. This may seem counterintuitive, but it is based on a calf starter with particle size providing the proper fermentation in the rumen to stimulate papillae development in the rumen wall. Hay is bulky, has a low rate and extent of digestion, causes some gut fill distorting true bodyweight gain and produces the wrong balance of volatile fatty acids (VFAs) in rumen fermentation for the best papillae development. These papillae in turn absorb the VFAs as their major energy source – just as occurs in adult ruminants.


Practical problems

One very practical common problem is failure to separate water and starter containers to eliminate calves dribbling water into starter and starter into water. This causes dirty water and wet feed, which reduces the calf’s intake of both. This can significantly reduce daily gain as seen in a study of calves in the month after weaning (Table 1).

043020 kertz tb 1

Another practical problem is inadequate starter intake by the time of full weaning. This can be due to poor starters (why I recommend a well-texturized starter), but it is most likely due to insufficient time and level of starter intake prior to weaning. In many cases, high milk or milk replacer feeding has not been reduced long enough for adequate starter intake before full weaning. There is an inverse relationship between milk and/or milk replacer fed and starter intake as seen in Figure 1. In a meta-analysis of 21 treatments from 9 individual calf studies, increasing dry milk and/or milk replacer intake by 0.2 pounds per calf daily decreased dry starter intake by 0.13 pounds per calf daily. A 2018 National Animal Health System (NAHMS) study of 104 US dairy farms in 14 states illustrated this very issue (Table 2).

043020 kertz tb 2

Both Holstein and Jersey heifer calves reached that double birthweight goal by 2 months of age. But, post-weaning daily gain for Holsteins decreased from 1.61 pre-weaned to 1.32 pounds. That indicates a major issue with the weaning transition period after full weaning in not having enough starter intake for a long enough period of time before full weaning for adequate rumen development. The Jerseys did not show the same falloff, but there were only 114 Jerseys versus 2,273 Holsteins in this database.

There was a similar fall-off for Holstein hip-height gain post-weaning, but again not for Jerseys. As a reference point, hip heights are about 2 inches greater than wither heights. As I found from a 5-year Holstein database published in 1997 and evaluation of growth patterns published in 1998 (Kertz et al.), height increase is very critical for the overall growth of Holstein heifers. The pattern for height increase should be that from birth to pre- first-calving height, 50% should occur in the first six months, 25% in the next six months and only 25% in the last 12 months.


Since this height increase is biologically controlled, primarily through growth hormone and age related just as in humans, as far as I have been able to determine, there is no compensatory increase for calves in height at a later age if not made within these age periods. During the first six months, wither height should increase about 2 inches monthly. It is sort of a make it then or lose it situation. These data indicate Holstein heifer calves were not making appropriate weight and height increases post-weaning, most likely due to a poor pre- and post-weaning transition program.

The amount of milk or milk replacer fed and sit energy and protein levels primarily affects starter intake. In turn, intake of starter, preferably in texturized form, determines how well the rumen is developed and how well calves perform post-weaning. The most recent NAHMS study indicates lower post-weaned daily gain than from pre-weaned daily gain. This is a largely unrecognized problem, and it is related to the third critical period. end mark

References omitted but available upon request. Click here to email an editor.

A. F. Kertz
  • A. F. Kertz

  • Andhil LLC
  • St. Louis, Missouri
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