Feeding Canola Meal to Cows and Heifers
There are few studies on the effect of RSM or CM supplementation on the effect of reproductive beef cattle. Hereford x Friesian cows fed three different protein sources, barley-urea, maize gluten and RSM + winter wheat straw ad libitum, for two consecutive years reported no difference in LW, condition score or calf birth weight (Pullar and Rigby 1993 {883}). A study began when heifers were 14-15 months old, lasted 5 months and were slaughtered when 6 wks pregnant. Hereford x Friesian heifers were supplemented with 250 g/kg extracted (22.5 mmol GL/kg DM), 320 g/kg expeller (28.8 mmol GL/kg DM) RSM or 210 g/ kg SBM (DM) to determine effects on reproductive parameters. Barley straw was the only roughage offered. Mean CP value of the diets was 182 g/kg and ME was 12.8 MJ/kg (DM). Inclusion of RSM did not effect palatability of the ration, liveweight gain, general health or pregnancy rate. However, foetuses from heifers fed RSM were smaller compared to heifers fed SBM. A study by Nisley and Brownson (1992 {963}) compared CM (21.3% CP, 67% TDN, 2.60 Mcal/kg ME) to cubed alfalfa (17.0% CP, 67% TDN, 2.29 Mcal/kg ME) when supplemented to heifers and cows. Forty-five crossbred 3 yr old heifers were fed 1.59 kg/d of beet pulp and 2 treatment groups received 1.59kg/d beet pulp + .91 kg/d of alfalfa cubes or CM. Heifers receiving CM gained more (P < 0.05) and had heavier calves than the other groups. Cows receiving both protein supplements had greater pelvic area growth. There were no differences in cow condition score or the dystocia score between treatments. One hundred thirty-three crossbred cows placed on pasture received 1.81 kg/d of alfalfa cubes or CM. Cows fed CM gained more, but there were no difference in cow condition score, calving data or dystocia score between cows fed the 2 protein supplements (Nisley and Brownson 1992 {963}). They concluded that CM supplementation produced greater weight gains in late gestation cows compared to alfalfa (Nisley and Brownson 1992 {963}; Dhuyvetter et al. 1992 {962}).
Heifers are raised for replacement
and slaughter. Overfeeding of pre-pubertal heifers may cause
an impairment of mammary growth resulting in reduced milk yields
(Foldager and Sejrsen 1991 as cited by Mäntysaari 1993 {927}).
Heifers raised for replacement have a target gain of 600-700g/d
and it is common to restrict energy intake. However, heifers
for slaughter can be placed on a high plane of nutrition and gains
of over 800g/d are normal. Finnish Ayrshire heifers (87 to 220
kg) were fed four diets, two diets at low feeding levels and two
at high feeding levels and protein sources urea and RSM were compared.
Protein source had no impact on ADG (692 vs. 655 g/d) on low
feeding intensity. On a high feeding intensity (ADG over 800
g/d) heifers (3-10 month old) under 220 kg liveweight were able
to improve ADG (805 vs 890 g/d; P < 0.01) when RSM replaced
urea as a protein source in a hay-barley diet. The better growth
rate of the heifers was caused by an increased total supply of
AA to the small intestine because the energy intake between the
two groups was similar. Heifers supplemented with RSM on the
high feeding level had a higher DM intake (3.74 vs. 4.07 kg/d;
P < 0.05) than heifers fed urea. The increase in hay intake
on the high RSM diet may be related to a higher fiber and OM digestion
of diets supplemented with slowly degraded proteins or it may
be explained by the increased growth and higher nutritional need
of the heifers on the high RSM diet. Blood urea concentrations
were higher with the supplementation of urea than with RSM indicating
a bigger loss of N from the rumen. For carcass quality grade
or dressing % no differences were found between energy levels.
Protein source did not affect body or slaughter measurements
of the heifers (Mäntysaari 1993 {927}). Canola meal can
be used as the sole source of protein for cows and heifers without
any adverse effects on reproduction.