Although there is no practical limitation
on the amount of CM which can be included in dairy cow rations,
the inclusion of more than 5% or 10% RSM (Mawson et al. 1993 {872})
should be avoided. Rapeseed meal is unpalatable and will interfere
with iodine use. Glucosinolate hydrolysis products can have a
marked effect on diet palatability/intake as reflected by growth
and production trends (Mawson et al. 1993 {922}). Rapeseed meal
is unlikely to be available in Canada but it is still used in
some countries and is available on the export market (Christensen
1998). Few reports indicate FI problems in dairy cattle when
fed LG-RSM or CM are fed (Mawson et al. 1993 {922}). Emanuelson
et al. (1993 {916}) and Ahlin et al. (1994 {875}) fed cows up
to 3.0 kg LG-RSM/c/d with positive performace on FI, feed conversion,
milk production and milk composition for 3 yrs. Feeding CM to
lactating dairy cows up to 20% (Song and Kennelly 1989 {1058})
or 30% can be recommended with no risk of feed refusal (Mawson
et al. 1993 {922}).
Effect on Milk Yield and Composition
Many short and long term experiments have been conducted
using CM as the main protein source for dairy cows with excellent
and often improved milk production (Hill 1991 {996}). Long term
studies conducted by Emanuelson et al. (1993 {916}) and Ahlin
et al. (1994 {875}) fed cows up to 3.0 kg LG-RSM/c/d with positive
effects on FI, feed conversion, milk production and milk composition
for 3 yrs. Rapeseed meal supplementation compared to SBM and
CSM and tallow resulted in increased milk protein content and
production (P < 0.10) (Emanuelson et al. 1993 {916}; 1990 {1034}).
Another study by Tuori (1992 {961}) fed dairy cows 0 to 33% RSM
in the concentrate mixture and direct cut grass silage and hay.
Milk production increased by 0.77 kg in milk or 0.70 kg in energy
corrected milk yield (P < 0.02) and in protein yield 27g/d/kg
increase in RSM DM (P< 0.01). Rapeseed meal supplementation
resulted in a linear increase in milk production until RSM levels
over 12-16%. The protein content of milk increased by 0.07g/kg
per MJ increase in metabolizable energy intake (P < 0.02).
Rapeseed meal was equivalent to SBM on the same CP basis in the
concentrate and there was no difference in milk yield. Heat-moisture
treatment of CM increased milk yield in one out of three experiments
(Tuori 1992 {961}). Over a two year lactation period 620 g/kg
RSM-00 (Dollar variety, 2 mol/g), 500 g/kg SBM and 760 g/kg sunflower
meal (containing 300 g CP/kg DM) were used as the main sources
of protein and daily milk yields were 26.7, 25.1 and 25.3 kg/d,
respectively. The three protein sources were determined to be
equivalent protein supplements (Vincent et al. 1990 {1007}).
Some short-term lactation studies are located in table 7.
| Table 7. Performance of Dairy Cows supplemented with CM and other protein sources in early lactation. | ||
| Reference | Diet | Performance |
| Early lactation studies | ||
| Rae et al. 1983 {1248} | Dietary CP% was 14.6 or 17.4 with CM increase in diet (13.0 + 23.5% CM DM) | CP with CM milk yield (33.2 vs. 30.4 kg/d; P<0.05), lactose, protein, fat yield, Total EAA |
| McClean and Laarveld 1991 {980} | Dietary CP was 15% supplied by 24% CM or 15% SBM (as fed) | -both proteins supplements were equivalent in maintaining milk production at approximately 30 kg/d |
| Robinson et al. 1991 {992} | 5 isonitrogenous diets (26 g of N/kg DM) replacing CM with Barlein | CM in milk yield with no effect on BWG or FI |
| DePeters and Bath 1986 {1142}+ 1985 {1179} | Two isonitrogenous diets (18% CP) using CSM and CM (12 and 13%) | = milk yield at 39.8 and 41.4 kg/d, respectively and no effect on milk composition or BW, FI |
| Harrison et al. 1989 {1069} | Replacing whole cotton seed with CM with at 3 increments | = milk yield at 40.7. 40.9 and 40.7 kg/d for diets containing 4, 10 and 15.5% CM |
A key to maximum dairy cow production is the provision of properly balanced rations and some studies have reported an increase in production from an increase in bypass protein from different protein sources or processing of CM. Dairy cows diets that differ in the rate and extent of protein degradation may influence milk yield and major components of milk (Khorasani et al. 1994 {806}). Holstein cows weighing 600 kg in early lactation showed a linear yield response to increasing inclusion of a protein source that had a higher bypass value, FM and gluten meal, in replacement of CM. However, no response to additional bypass protein was observed for first time lactation heifers. The additional 3.3 kg of milk yield may have resulted from the increased protein from FM and corn gluten meal passing to the intestine or a direct effect of those protein sources on microbial growth and ruminal digestion. Although it was not significant cows fed the higher bypass diet had greater persistency of milk yield than those fed the lower bypass protein (Khorasani et al. 1996 {806}). Other studies have indicated a response to bypass protein independent of a dietary CP increase (Murphy et al. 1986 {1146}; {1147}; {1150}).
Studies by Huhtanen et al. (1995 {839}; 1991 {971}) compared CM to dried and wet distillers' solubles. Supplementation of 1.5 kg/d of heat treated CM to Friesian cows fed grass silage and a grain concentrate increased silage intake and total DM intake by approximately 0.5kg/d; (P< 0.05), milk yield, protein content and fat yield and LWG (Huhtanen et al. 1991 {971}; 1995 {839}). Replacement of CM with FA-treated dried distiller's solubles resulted in lower LWG and milk protein, but equivalent milk yield (Huhtanen et al. 1991 {971}). There was no interaction when CM was supplemented to a starchy or fibrous concentrate energy source (Huhtanen et al. 1995 {839}).
Other studies have reported protein source and an effect on milk composition. Incorporating CM into the diet at 12% of concentrate to dairy cows grazing on pasture resulted in equivalent milk production in comparison to cows supplemented with 0.9% urea in concentrate (about 27 kg/d). The fat content was equivalent (39 g/kg) between groups but CM supplementation increased milk protein and lactose in comparison to urea based diets and the cereal by product control (Tesfa et al. 1995 {819}). Dietary CP levels of 13, 15, 17 and 19% DM were achieved by replacing barley with CM (0, 12, 24 and 36% concentrate) in the diet of early lactating Holsteins. Maximum microbial protein synthesis occurred at 15% CP. Protein levels in excess of 15% resulted in increased rumen ammonia levels, blood urea and duodenal total nitrogen supply. Milk composition and yield (28 kg/d) were not influenced by dietary protein level with the exception of milk protein percent that was higher at 15% CP than at other protein levels. Cows fed 13% CP lost BW and those with higher a CP % gained (Ha and Kennelly 1983 {1241}; Ha and Kennelly 1984 {1218}). A comparable study by Gonda (et al. 1994 {856}) using RSM-00 increased dietary CP from 14.3 to 19% increasing milk production, milk protein, increased feed and energy utilization. Milk fat was significantly less for the group receiving 14.3% CP. Comparable results were reported by Boer and Kennelly (1988 {1095}).
Studies done in late lactation. Song and Kennelly (1989 {1058}) incorporated 10% CM, barley silage supplemented with urea or ammoniated barley silage into mixed rations for late lactation cows and found no effect on milk yield and composition. In another study by Robinson and Kennelly (1988 {1096}; {1101}) Holstein cows in late lactation fed a mixed diet (16% CP) replaced CM with corn gluten meal without an effect on milk yield or composition or DMI. Late lactation cows fed 24.6% CM or solvent linseed meal in the concentrate, reported equivalent milk production (about 13 kg/d). Canola meal supplementation with barley or corn resulted in a higher milk fat percentage without an effect on the rest of the milk composition parameters (Khorasani et al. 1994 {858}).
In conclusion, CM can be used in all stages of milk
production as the main protein source and with properly balanced
rations superior or equivalent milk yield is expected even in
comparison to more common or traditional protein supplements (e.g.
SBM or CSM).
Canola meal as a protein supplement in brown-shelled egg layer rations may result in eggs with a fishy odor. Bacterial fermentation in the caecum of poultry results in the conversion of sinapine and choline to trimethylamine, which is deposited in the eggs. It has been implicated in fishy flavored milk from cows grazing wheat pasture containing high levels of choline. The concentration of choline in CM is approximately twice that found in SBM, however measurements of trimethylamine in milk from cows fed CM indicated that choline levels present in CM did not significantly increase milk levels compared to SBM. Animals fed high levels of choline had increased levels of TMA in milk and rumen fluid, however the relationship was not a linear one (Pinnell and Kennelly {749}). Mawson et al. 1995 {834} reported that there are few reports of an off flavor due to supplement of LG-RSM or CM and that GL products in the milk of LG-RSM would be in the safe range for human consumption (Mawson et al. 1995 {834}). Emanuelson et al. (1993 {916}) reported an increase in thiocyanate content and a decrease in I with a medium to high (1.2-2.5 kg DM) RSM supplementation. This is in agreement with McClean and Laarveld (1991 {980}; 1988 {1084}) that fed CM containing 13.38 mol/g GL (as fed).
Protein sources effect the composition of milkfat
for cheese manufacture. Canola meal offered as a protein source
produced a milkfat with significantly lower solid fat content
and higher unsaturated fatty acid content compared with milk from
cows offered CSM or lupin (Rowney and Christian 1996 {797}).
Effects on Physiological and Reproductive Parameters
It is the breakdown of GL by myrosinase into products that are goitrogenic that are responsible for the antithyroid (hypothyroidism) activity of RSM. Thiocyanates, isothiocyanates and nitriles are capable of depressing iodine uptake, iodification, T3:T4 ratios and thyroid histology (Bell 1984 {1232}). A common finding with feeding HG-RSM is reduced iodide (I) levels and higher thiocyanate (SCN-) concentrations in milk and lower levels of T4 in serum (Bell 1984 {1232}; Emanuelson et al. 1993 {916}).
A relationship between hypothyroidism and subfertility or infertility will appear when the hypothyroid condition is severe enough to produce a clinically observable change in the thyroid function (Ahlin et al. 1994 {875}). Vincent et al. (1988 {1104}) fed heifers 2 different levels (250 g/kg extracted -yr 1 and 320 g/kg expeller-yr.2) of HG-RSM for two 5-month periods over 2 years found histological evidence of goitrogenicity (but no weight change), significantly elevated plasma levels of SCN-, and depressed levels of plasma thyroxin T4. In another study, high levels of GL (31 mol/g DM of the 00-RSM) was the explanation given for the minor and compensated depressed fertility and thyroid function that occurred in the first batch of primiparous cows. Thyroid glands of heifers given RSM showed histological evidence of goitrogenicity. For primiparous cows the interval from calving to conception tended to be longer for the cows fed the high rate of RSM-00 and had the higher number of AI/conception and the longest calving interval. These findings were trends, not significant and were not found in the next two lactations (Emanuelson et al. 1993 {916}). The disturbed fertility of the first calvers in the study confirms that the younger and still growing, first calvers are more sensitive to GL (Ahlin et al. 1994 {351}; Emanuelson et al. 1993 {916}).
Emanuelson et al. (1993 {916}; {1108}; {1201}; {1074}),
Ahlin et al. (1994 {351}) and Mawson et al. (1995 {871}) report
that feeding 00-rapeseed products from certified double low varieties
to adult dairy cows in amounts up to 3 kg RSM/d/cow will not have
any negative effects on animal health or fertility over a long
term study for cows. Ahlin et al. 1994 {875} reported over the
three year experiment calving age, calving season and experimental
year had a much greater influence on both fertility and thyroid
function than dietary group. With the introduction of LG-RSM
or CM incorporation rates have increased up to 24% of the diet
without any impairment on reproduction parameters (Mawson et al.
1994 {871}).