ABSTRACT Metabolizable energy (ME) is the most limiting nutrient for milk production in pastoral systems. In Chile, using four wethers and grass cut on six measurement dates, Garrido and Mann (1981) developed an equation to predict grass ME concentration based on content of in vitro digestible organic matter in DM. The application of the Garrido and Mann (1981) equation has been generalized in Chile for all feed ingredients, diets and ruminant species. We hypothesized that ME prediction from this equation has limitations for its use in lactating grass-fed dairy cows. The objective of this study was to validate the ME prediction equation by Garrido and Mann (1981) for lactating grass-fed dairy cows in the autumn and spring seasons. The study was conducted at INIA Remehue (Osorno, Chile) using two sets of eight Holstein Friesian cows, with each group used twice in 21-d experimental periods in autumn and spring, respectively. Fresh grass-only diets with a predominance of perennial ryegrass (Lolium perenne L.) were supplied through soiling. In the last 5 d of each period, grass ME concentration was measured by subtracting energy lost in feces, urine and methane from ingested gross energy. A weak linear relationship was obtained between the ME determined in trials and ME predicted from the Garrido and Mann (1981) equation (R2 = 0.266; P = 0.003). The ME prediction equation currently in use is inadequate for lactating grass-fed dairy cows. Therefore, new and improved equations for estimating grass ME specific to dairy cows are needed.

ABSTRACT Dietary supplementation with concentrates is regarded as an effective strategy to decrease the intensity of methane (CH4) emissions, although it has rarely been evaluated in late lactation dairy cows. The aim of the present study was to investigate the effects of two levels of dietary concentrate supplementation on CH4 emissions and milk production and composition of dairy cows in late lactation. The study was conducted using 24 multiparous Holstein Friesian cows in late lactation (253 ± 18 d in milk), and had a duration of 3 wk, including 2 wk of adaptation to the diet and 1 wk of measurements. Treatments consisted of two levels of concentrate supplementation (4 vs. 8 kg d-1 cow-1; as-fed) offered daily in two equal rations during milking. In addition, diets included 2 kg DM grazed grass and 8 kg as-fed of grass hay. In week 3 of the study, CH4 emissions were measured for 7 consecutive days using the sulfur hexafluoride tracer technique. Average total DM intakes for the cows fed the 4 and 8 kg concentrate treatments were 12.3 and 15.6 kg DM, respectively. Treatments had no effect on milk yield, milk fat, or milk lactose concentrations. Milk protein concentration tended to increase in cows offered 8 kg of concentrate. Higher concentrate intake tended to increase cow body mass gain, but not condition score change. The 8 kg treatment increased total CH4 emissions (g d-1) by 10.7%, whereas CH4 yield (g kg-1 DM intake) was decreased by 12.7%. Methane intensity (g kg-1 milk yield) was unaffected by treatments. Dietary concentrate supplementation for late lactation cows is ineffective in mitigating CH4 emission intensity, because animals do not respond with an increase in milk production.

ABSTRACT: Canola provides oil for human consumption and a by-product from the extraction of its oil canola meal (CM), is used as a good quality protein and lipid supplement for ruminants. The aim of this study was to determine the chemical composition and fermentation profile associated with the potential for methane production of three types of CM: solvent-extracted CM of Brassica napus (CMBN), B. juncea (CMBJ) and cold press-extracted CM from B. napus (CPCM) used to feed ruminants. The protein content of canola meal ranged from 36 to 41 %. The acid and neutral detergent insoluble in nitrogen ranged from 1 to 2 % and 4 to 5 %, respectively. The lipid content of canola meal samples ranged from 2 % (CMBN, CMBJ) to 14 % (CPCM). In vitro, dry matter disappearance of CMBJ was higher than that of other types of CM at 4 h, 24 h and 48 h. Gas production from CMBJ was greater than that of CPCM and CMBN at 24 h and 48 h of incubation. CPCM produced lower methane than CMBJ at 48 h of incubation. CPCM produced a higher (p < 0.05) molar proportion of propionate from 12 h to 48 h of incubation. In conclusion, this study found that CPCM could be a good source of protein (mainly PB2) and lipids in the feed of ruminants; it will decrease methane production and enhance propionate production. There was correlation between less methane production, and the content of lipids and PB2 in the three types of CM studied.

This paper reviews how tannins, through their effects on rumen lipid metabolism, can affect the composition of ruminants’ meat and milk fat. Tannins are a heterogeneous group of plant secondary compounds known for both beneficial and detrimental effects on animals’ digestive physiology. Tannins supplementation of ruminants’ diets alters both in vivo and in vitro unsaturated fatty acids biohydrogenation and hence the profile of fatty acids outflowing the rumen, which can influence milk and meat content of beneficial fatty acids such as linolenic acid (c9,c12,c15-18:3), vaccenic acid (ti 1-18:1) and rumenic acid (c9,t11-18:2), among others. Published information indicates that tannins could inhibit biohydrogenation though affecting ruminal microorganisms. Some studies found increments in linolenic, rumenic and/or vaccenic acids in meat and milk fat using different sources of tannins; however, the effects of tannins supplementation on milk and meat fatty acid profile are not consistent, and there are contradictory results published in the literature. Effects of tannin supplementation on fatty acids biohydrogenation are affected by the chemical type of tannins, the complexity of their interactions with dietary components, and the potential microbial adaptation to tannins. In addition, the duration of the tannins-feeding period may also affect milk and meat fatty acid profile. Characterizing the effects of each specific tannic compound on different biohydrogenation steps and on the microbial species conducting them, as well as the interaction between specific tannin compounds and other dietary components can help to take greater advantage of tannins potential to contribute to improve human health through promoting beneficial fatty acids in ruminants products.