Effect of level of oil inclusion in the diet of dairy cows at pasture on animal performance and milk composition and properties

Abstract

The effect of including additional oil, incorporated as whole rapeseeds, in the diet of 64 Holstein-Friesian dairy cows (32 mid-and 32 late-lactation) at pasture on animal performance and milk fat composition and properties was followed over a continuous trial of 20 weeks duration. Within two stages of lactation (mid, 130 ± 16.2 days, or late, 231 ± 58.9 days), cows were allocated to concentrate treatments representing four levels of rapeseed oil inclusion, 0 (control), 200, 400 and 600 g oil day −1 . Oil inclusion had little effect on milk yield but decreased milk fat content significantly (P < 0.01), with a mean depression of 0.40% at the highest level of oil inclusion. The content of milk protein also decreased with increasing addition of oil, but the decrease was smaller than the milk fat depression and was not statistically significant. Increasing the level of rapeseed oil in the diet to 600 g oil day −1 resulted in linear changes in milk fat and protein concentrations which were described by regression equations. For each 100 g of rapeseed oil added to the diet, milk fat content decreased by 0.068% in mid-lactation cows and 0.061% in late-lactation cows, while protein content decreased by 0.026% in mid-lactation cows and 0.028% in late-lactation cows. Total unsaturated fatty acid content of milk fat also increased in a linear fashion with increased level of oil addition, from 345.7 g kg −1 total fatty acids in control milk fat to 459.3 g kg −1 total fatty acids at 600 g oil day −1 , while total saturated fatty acids decreased in the same milk fats from 640.7 to 522.2 g kg −1 total fatty acids. These changes were reflected in lower solid fat contents (SFC) in the milk fat at the lower temperatures of measurement, eg 41% SFC at 5 • C at the highest level of oil inclusion compared with 52% in the control milk fat. However, SFC at 20 • C showed little difference with increasing level of dietary oil addition, an important factor in maintaining product integrity at room temperatures. The relatively high content of the monounsaturated fatty acid C18:1 (345.5 g kg −1 total fatty acids at 600 g oil day −1 ) and low content of polyunsaturated fatty acids (total C18:2 and C18:3 <40 g kg −1 total fatty acids at 600 g oil day −1 ) ensured that the oxidative stability of the treatment and control milk fats did not differ significantly. Stage of lactation had an unexplained effect of consistent magnitude on milk fat composition throughout the trial period, with late-lactation animals producing milk fats containing a significantly (P < 0.001) higher proportion of unsaturated fatty acids than the mid-lactation animals. Changes in the proportions of unsaturated fatty acids in milk fat, as reflected by changes in iodine value, were established within 2 weeks of the trial commencing and persisted over the 20 weeks of the trial duration. No adverse effect on animal health from this type of dietary manipulation was identified.

Supplementation with corn oil and palm kernel oil to grazing cows: ruminal fermentation, milk yield, and fatty acid profile

“…In this study, milk fat yield (g d −1 ) from de novo synthesized FA (≤ 17 carbons) was similar among treatments (423, 459, 474 g d −1 for C, CO, and CO:PKO, respectively); thus, this mechanism seems unlikely, according to the higher level of unsaturated FA for the oil treatments compared with control. Several studies suggest that fat supplementation reduces the concentration of milk protein (Zhang et al, 2006) with an increase in its yield (g d −1 ) due to a greater milk production (Fearon et al, 2004;Flowers et al, 2008). In this study, protein concentrations in milk were similar among the treatments regardless of the addition of oils to the diet.…”

Conjugated linoleic acid content in milk of Chilean Black Friesian cows under pasture conditions and supplemented with canola seed (Brassica napus) concentrate

“…Lerch et al (2012a) observed higher milk fat contents in cows receiving cold-pressed fat-rich canola seed meal and whole unprocessed canola seeds compared with other treatments. On the other hand, in grazing studies, the inclusion of whole fat canola seeds resulted in a decreasing on milk fat content (Murphy et al, 1995;Lawless et al, 1998;Fearon et al, 2004), while the study reported by Lerch et al (2012a) showed that whole unprocessed canola seeds increased milk fat content when compared with the control treatment. Regarding to the protein content, some of these authors (Lawless et al, 1998;Chichlowski et al, 2005;Lerch et al, 2012a) reported a decreasing in the percentage of milk protein with the use of canola seeds.…”

“…Likewise, supplementation of dietary fat can decreasing the percentage of milk protein. Hence, presentation of the canola seeds as whole oilseeds is employed to minimise adverse effects of unsaturated dietary lipid on rumen microbial activity and possibly provide some measure of protection for the unsaturated oilseed fatty acids from ruminal biohydrogenation (Fearon et al, 2004). In this respect, Murphy et al (1990) observed that feeding unground, intact canola seeds in an unpelleted concentrate to dairy cows resulted in the passage of a proportion of unbroken seeds through the digestive tract into the faeces and that, in this form, the oilseeds had less impact on milk fat composition than ground canola seeds.…”

“…Within the seeds of oilseeds, rapeseed (Brassica napus) has been used in TMR (total mixed ration) diets in dairy cows (Bayourthe et al, 2000, Chouinard et al, 2001Ward et al, 2002;Chichlowski et al, 2005;Chen et al, 2008;Neves et al, 2009;Lerch et al, 2012b). However, the information about its utilization as a supplement under grazing conditions is limited and contradictory (Stanton et al, 1997;Lawless et al, 1998;Fearon et al, 2004;Lerch et al, 2012b). In Chile, Chilean Black Friesian (Holstein × Black Friesian) is the most important dairy breed and produces almost 80% of cow's milk receptioned on dairy industry (INE, 2007).…”

Milk quality – a future approach from a researcher’s point of view

“…Thus, it is possible to obtain milk fat with a high proportion of oleic acid (C18:1) on diets with high content of oleic acid (C18:1) and/or diets with high content of polyunsaturated acids which are desaturated to stearic acid (C18) in the rumen. A realistic goal is about 30 to 25% oleic acid (C18:1) in the milk fat at pasture and on indoor feeding with grass silage, respectively, assumed supplementing with an appropriate fat source (Fearon et al, 2004;Ryhänen et al, 2005).…”