Milk production responses, rumen fermentation, and blood metabolites of dairy cows fed increasing concentrations of forage rape (Brassica napus ssp. Biennis).

The aim of this study was to determine animal performance, rumen fermentation, and health-related blood metabolites of dairy cows in mid lactation fed with increasing levels (30 and 45%) of forage rape (FR) in the diet. Twelve pregnant multiparous lactating Holstein-Friesian dairy cows were randomly allocated to 1 of 3 dietary treatments in a replicated 3 × 3 Latin square design. The experiment was divided into three 21-d periods. For the control diet, 13.0 kg (dry matter, DM) of grass silage, 3.0 kg DM of commercial concentrate, 2.7 kg of DM cold-pressed extracted canola meal, and 0.45 kg DM of solvent-extracted soybean meal were offered daily. For the other two treatments, 30 and 45% of the DM from silage, canola meal, and commercial concentrate were replaced in equal proportions with FR. Data were analyzed individually using linear and quadratic orthogonal polynomials. Ingestive behavior was altered by the inclusion of FR. We observed a linear increase in eating time at the expense of rumination time. Nevertheless, total DM intake was not affected by dietary treatments, averaging 19.5 ± 0.24 kg of DM/d. Milk yield increased linearly with increasing concentration of FR in the diet. Thus, feed efficiency of cows (kg of milk/kg of DM intake) increased linearly with the percentage of FR in the diet. Inclusion of FR in the diet had no effect on milk composition or milk sensory characteristics. Mean rumen pH of cows decreased linearly from the control to the 45% FR diet; however, dietary treatments had no effect on the daily amount of time that rumen pH was below 5.8 (252 ± 71.4), indicating no risk of subacute ruminal acidosis. Concentrations of total volatile fatty acids in the rumen and molar proportions of acetate and butyrate were increased with FR inclusion, whereas the proportion of propionate was linearly reduced. Excretion of uric acid and total purine derivatives tended to be greater for cows fed FR, which resulted in a trend toward a linear increase in estimated microbial N flow. However, N use efficiency was not affected by FR inclusion. Although differences for some hematological measures (increased white blood cell and neutrophils counts) and a quadratic response for glutamate dehydrogenase for cows fed FR in the diet (decreased with inclusion of 30% and increased with 45% in the diet) were observed, all values were within appropriate ranges for dairy cows. These results indicated that including FR to dairy cow diets, up to 45% of diet DM, improved milk production due to changes in volatile fatty acids and predicted microbial N flow and had no negative effects on dairy cow health or sensory characteristics of milk.

Milk production responses and rumen fermentation of dairy cows supplemented with summer brassicas.

Forage brassicas, such as summer turnip (ST; Brassica rapa) and forage rape (FR; Brassica napus), are used as supplementary crops during summer. However, studies with lactating dairy cows fed these forages are limited and report inconsistent productive responses. The aim of this study was to determine dry matter intake, rumen fermentation and milk production responses of dairy cows in mid-lactation supplemented with and without summer ('ST' or 'FR') brassicas. Twelve multiparous lactating dairy cows were randomly allocated to three dietary treatments in a replicated 3 × 3 Latin square design balanced for residual effects over three 21-day periods. The control diet consisted of 16.2 kg DM of grass silage, 2.25 kg DM of commercial concentrate and 2.25 kg DM solvent-extracted soybean meal. For the other two dietary treatments, 25% of the amounts of silage and concentrates were replaced with FR or ST. The inclusion of forage brassicas had no effects on milk production (24.2 kg cow/day average) and composition (average milk fat and protein 43.2 and 33.6 g/l, respectively). Dry matter intake was 0.98 kg and 1.12 kg lower for cows supplemented with FR and ST, respectively, resulting in a greater feed conversion efficiency (1.35 kg milk/kg DM for ST and FR v. 1.27 kg milk/kg DM for the control diet). Intraruminal pH was lower for cows supplemented with ST compared to the control diet; however, it did not decrease below pH 5.8 at any time of the day. After feeding, the concentrations of total short-chain fatty acids (SCFAs) in rumen contents increased with ST supplementation compared to the control diet. Inclusion of FR in the diet increased the molar proportion of acetate (68.5 mmol/100 mmol) in total SCFA at the expense of propionate, measured 6 h after feeding of the forage. The molar proportion of butyric acid was greater with ST and FR supplementation (13.1 and 12 mmol/100 mmol, respectively) than in control cows. The estimated microbial nitrogen (N) flow was 89.1 g/day greater when supplementing FR compared to the control diet. Based on the haematological measures, the inclusion of summer brassica forages did not affect the health status of the animals. These results indicate that mid-lactation dairy cows fed brassicas are able to maintain production despite the reduced intake, probably due to improved rumen fermentation and therefore nutrient utilization.