Elston et al., 1989; Morant and Granaskthy, 1989) but, as with the Woods’ equation, their use with beef cattle milk production has been very limited because of the relatively large number of data points to fit the equation form. Jenkins and Ferrell (1984) proposed a similar equation form:

Eq. 4–11

where Yn equals daily milk yield (kg/day) at week n postpartum, a and k are solution parameters, and e is the base of natural logarithms. This equation may be used to estimate the following values:

Eq. 4–12

Eq. 4–13

Eq. 4–14

This equation form has been criticized (Hohenboken et al., 1992) but has an advantage over that of the Woods’ equation in that it can be fit with a minimal number of data points. In addition, curve parameters may be estimated from published data with a minimum of information.

Available data (Deutscher and Whiteman, 1971; Jeffery et al., 1971; Kropp et al., 1973; Totusek et al., 1973; Grainger and Wilhelms, 1979; Neidhardt et al., 1979; Gaskins and Anderson, 1980; Chenette and Frahm, 1981; Jenkins and Ferrell, 1984; Holloway et al., 1985; Jenkins et al., 1986; Clutter and Neilson, 1987; Sacco et al., 1987; Lubritz et al., 1989; Mezzadra et al., 1989; McCarter et al., 1991; Hohenboken et al., 1992; Jenkins and Ferrell, 1992) indicate that peak lactation occurred at approximately 8.5 weeks postpartum in cows with suckling calves. Those data included a wide variety of breeds or breed crosses of cows, calves, milk yields, and sampling protocols. This value is somewhat later than generally observed for dairy cows and may reflect the influence of calf consumption capacity. Rearrangement of Eq. 4–12 yields

Eq. 4–15

Maximum or peak yield of cows with suckling calves is variable, as noted above. Reported values range from about 4 to 20 kg/day. The highest values have been reported for Holstein or Friesian cows. More typically, reported values for dual purpose or dairy×beef crossbred cows have rarely exceeded 14 kg/day. Therefore, for the purposes of this publication, NEm and net protein requirements are for peak yield values of 5, 8, 11, and 14 kg/day for four types of cows typical of beef production enterprises (Tables 4–4 and 4–5). Rearrangement of Eq. 4–13 and solving for “a” yields estimates of 0.6257, 0.3911, 0.2844, and 0.2235 for cows having maximum yields of 5, 8, 11, and 14 kg/day at 8.5 weeks postpartum. Substitution of these values

TABLE 4–4 Net Energy (NEm, Mcal/day) Required for Milk Production

Week of Lactation

Peak Milk Yield, kg/day

5

8

11

14

3

2.42

3.87

5.32

6.77

6

3.40

5.44

7.48

9.52

9

3.58

5.73

7.88

10.03

12

3.36

5.37

7.39

9.40

15

2.95

4.72

6.49

8.26

18

2.49

3.98

5.47

6.96

21

2.04

3.26

4.48

5.71

24

1.64

2.62

3.60

4.58

27

1.29

2.07

2.85

3.62

30

1.01

1.46

2.19

2.83

NOTE: Requirement assumes milk contains 4.0% fat, 3.4% protein, 8.3% SNF, and 0.72 Mcal/kg.

TABLE 4–5 Net Protein (g/day) Required for Milk Production

Week of Lactation

Peak Milk Yield, kg/day

5

8

11

14

3

115

183

252

321

6

161

258

354

451

9

170

272

373

475

12

159

254

350

445

15

140

223

307

391

18

118

188

259

330

21

97

154

212

270

24

68

124

170

217

27

61

98

135

172

30

48

77

105

134

NOTE: Requirement assumes milk contains 3.4% protein.

into Eq. 4–14 yields estimates of total milk yield over a 30-week lactation period of 701, 1,122, 1,543, and 1,963 kg. These values encompass nearly all reported values for total milk yield of beef cows with suckling calves. Expected maximum milk production is highly dependent on cow genotype and is about 26 and 12 percent lower for 2- and 3-year-old heifers, respectively, than for cows 4 years old or older (Gleddie and Berg, 1968; Gaskins and Anderson, 1980, Hansen et al., 1982; Butson and Berg, 1984a,b; Clutter and Nielson, 1987).

Insufficient data are available to fully characterize the effects of age and breed of cow, stage of lactation, nutritional status, etc., on milk composition in beef cows. Therefore, for general purposes, mean of composition values for beef cows (Melton et al., 1967; Wilson et al., 1969; Kropp et al., 1973; Totusek et al., 1973; Cundiff et al., 1974; Holloway et al., 1975; Lowman et al., 1979; Bowden, 1981; Chenette and Frahm, 1981; Grainger et al., 1983; Mondragon et al., 1983; Butson and Berg, 1984a,b; McMorris and Wilson, 1986; Daley et al., 1987; Diaz et al., 1992; Masilo et al., 1992) is assumed. The average (mean±SD) value for milk fat was 4.03±1.24 percent (18 studies), for milk protein was 3.38±0.27 percent (10 studies), for solids



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