Grazing cows are more efficient than zero-grazed and grass silage-fed cows in milk rumenic acid production

Abstract

Six rumen-cannulated Holstein cows in early lactation were assigned to 3 treatments: grazing (G), zero-grazing (ZG), and grass silage (GS) harvested from the same perennial rye grass sward in a 3 x 3 Latin square design with three 21-d periods. The objectives of this study were to investigate the underlying mechanisms for the reported elevation in milk rumenic acid (RA) concentration associated with G compared with ZG and GS, and to identify the important variables contributing to the milk RA response. Grazing animals were offered 20 kg of dry matter/cow per day; indoor animals were offered ad libitum grass or silage. A concentrate at a rate of 3 kg/d was also offered to all cows. Rumen, plasma, and milk samples were collected in the third week of each period. Data were analyzed by the MIXED procedure of SAS. Dry matter intakes were less for GS with no difference between G and ZG. Milk yield was greater for G than for ZG or GS. Milk fat and protein contents were less for GS with no difference between G and ZG. The combined intake (g/d) of linoleic and linolenic (18:3n-3) acids was different across the treatments (G: 433; ZG: 327; and GS: 164). Rumen pH was less for G with no difference between ZG and GS. Concentrations of volatile fatty acids and ammonia nitrogen in rumens were not different across the treatments. Wet rumen fill was less for G with no difference between ZG and GS. Vaccenic acid concentrations were different across the treatments in rumen (G: 12.30%, ZG: 9.31%, and GS: 4.21%); plasma (G: 2.18%, ZG: 1.47%, and GS: 0.66%) and milk (G: 4.73%, ZG: 3.49%, and GS: 0.99%). Milk RA concentrations were greater for G (2.07%) than for ZG (1.38%) and GS (0.54%). Milk desaturase index based on the ratio cis-9-14:1/14:0 was not different across the treatments. Milk RA yield per 100 g of linoleic acid and linolenic acid intake (efficiency) was 2.23, 1.50, and 0.62 g in G, ZG, and GS, respectively, suggesting that G cows were more efficient than ZG and GS cows in milk RA production. Stepwise regression analysis of a group of variables revealed that plasma vaccenic acid accounted for 95% of the variation in milk RA production. Milk desaturase index did not enter into the model. Overall findings suggest that substrate intake influenced milk RA production but it was not the only factor involved. There were differences in efficiency of milk RA production, which appears to depend on the factors regulating ruminal vaccenic acid production and its supply to the mammary tissue.

Efecto de la edad de rebrote sobre el perfil de ácidos grasos en gramíneas tropicales

“…Los estudios revisados indican que aproximadamente un 75 % de la variabilidad en el contenido de ALC en la leche se puede explicar por el consumo total de sus precursores (ácido linoleico y linolénico) presentes en el alimento (Mohammed et al 2009). …”

Effect of grain type and processing method on rumen fermentation and milk rumenic acid production

“…In most studies, rumen pH measurements were generally taken either once (Tajima et al, 2001), twice (Abughazaleh et al, 2003;Mohammed et al, 2009), four times (Klieve et al, 2003) or six times a day (Kalscheur et al, 1997;Kim et al, 2008). It proved difficult to relate the selected pH measurements to changes in rumen bacterial population (Klieve et al, 2003;Kim et al, 2008), or to specific fatty acid (FA) metabolite (ruminal t10-18:1; Mohammed et al, 2009). Therefore, in this study we utilized a continuous rumen pH monitoring system (Penner et al, 2006) to determine rumen pH changes more accurately and relate them to the PUFA intermediates in the rumen.…”

“…Rumen samples for FA analysis consisted of both fluid and solids and were collected at the same time as described for VFA and NH 3 analyses and stored at 2208C. For FA analysis, the samples were freeze-dried and milled and 0.5 g of the sample pooled by cow each period was utilized for FA analysis following the protocol described by Mohammed et al (2009).…”

“…FA composition was determined from plasma samples pooled by cow each period. Plasma lipids were extracted, methylated and analyzed by GLC as described by Mohammed et al (2009).…”

Grazing increases the concentration of CLA in dairy cow milk

“…The most recent studies have shown that endogenous synthesis contributes a large proportion of total CLA in milk, with estimates including 64 (Griinari et al, 2000), 78 (Corl et al, 2001), 94 (Kay et al, 2004) and 93% to 97% (Piperova et al, 2002;Mohammed et al, 2009), depending on diet composition, oil supplementation and grazing. However, reasons for increased synthesis with regimens that are known to be effective in increasing milk CLA remain unclear.…”