The effects of three fat supplements on milk yield and composition were measured using 12 mid-lactation in-calf Hoistein-Friesian cows in a balanced incomplete change-over design over three periods each of 3 weeks. All cows received a basal diet consisting of 36 kg/day grass silage (dry matter (DM) 270 g/kg, metabolizable energy (ME) 11·6 MJ/kg DM) and 7 kg/day o f a concentrate mixture containing (g/kg) rolled barley (501), molassed sugar-beet pulp shreds (277), soya-bean meal (208) and a standard cow mineral supplement (14). Treatments were CON (control-no supplement); LIN and FISH (250 gl day of either linseed oil or marine oil, providing approximately 0·046 of ME intake) or TOA (95 glday of tuna orbital oil, providing 0·018 of total ME intake).There were no significant effects on silage DM intake or milk yield (means 9·25 and 17·2 kg/day respectively). The FISH and TOA treatments depressed (F < 0·05) milk fat concentration (45·4, 44·6, 34·5 and 41·6 (s.e.d. 1·08) g/kg for CON, LIN, FISH and TOA respectively; note — the same treatment order is used for all results quoted). Compared with values for CON, yield of f at (glday) was significantly (F < 0·05) greater for LIN and significantly lower for FISH (739, 808, 572 and 732, s.e.d. 28·7). All three oil supplements reduced (F < 0·05) milk protein content (33·6, 32·5, 30·6 and 32·4 (s.e.d. 0·43) g/kg) but, apart from a small increase for LIN, protein yield (glday) was unaffected (545, 586, 510 and 574, s.e.d. 20·2).The concentrations (g/100 g) of short-chain fatty acids (< C14) and C16 : 0 in milk f at were lower (F < 0·05) for LIN than for the other treatments. All supplements increased the concentrations ofC18:1 (F < 0·05), the value for LIN being greater (F < 0·05) than for the other treatments (21·0, 27·2, 25·3 and 23·7, s.e.d. 0·74). The FISH and TOA treatments increased (F < 0·05) the concentrations of long chain (< C2O) (n-3) poly-unsaturated fatty acids (PUFA), (0·19, 0·17, 0·49 and 0·27, s.e.d. 0·026) but less than proportionately 0·03 of dietary intake of these acids was transferred to milk, probably because they were found to be mostly in the phospholipid and cholesterol ester fractions of plasma. The FISH and TOA treatments increased (F < 0·05) the percentages of total trans fatty acids in milk fat (1·13, 2·19, 10·26 and 3·62, s.e.d. 0·728) whilst a significant (F < 0·05) increase in conjugated linoleic acid (CLA) was observed only for FISH (0·16, 0·28, 1·55, and 0·52, s.e.d. 0·154). Concentrations of CLA and total trans acids in milk were highly correlated (r = 0·91, no. =36, F < 0·001) whilst trans acids in milk were inversely correlated with milk fat content (r = -0·63, no. = 36, F < 0·001) supporting the theory that milk fat depression may be caused by increased supply of trans fatty acids to the mammary gland. The health implications of these changes in milk fat composition are discussed.

No abstract

The potential of the spot urine sampling technique as an alternative to performing a total urine collection was evaluated. Twelve multiparous Holstein-Friesian cows were given two experimental diets in a complete change-over design using two 14-day experimental periods. Experimental diets were either silage offeredad libitumwith 7 kg fresh weight concentrate supplement as a single meal (SF), or a complete diet formulated from the same ingredients with a similar foragexoncentrate ratio (CD). Total urine collections were performed every 2 h on days 11 and 14 of each experimental period. Subsamples of urine were stored at 20°C and subsequently analysed by high-performace liquid chromatography. Daily allantoin and purine derivative (PD) excretion were highly correlated (r = 0·995, no. = 48,P< 0·001). PD and creatinine excretion during each 2-h interval depended on time of collection (PD,P< 0·001 and creatinine,P< 0·05) and on cow (P< 0·01) but were unaffected by sampling day or treatment. Diurnal variations in the molar ratio ofPD or allantoin to creatinine (PD/c and Ale, respectively) followed similar diurnal patterns as observed for PD and allantoin excretion. The data were used to assess the error of prediction of daily mean PD/c or Ale ratios. Three spot sampling regimens (based on the collection of four 4-h samples, three 8-h samples or two 12-h samples) and also on either single or 2-day urine collections were evaluated. Collection of multiple samples within a day was more reliable than collecting fewer samples over several days. Prediction errors were greater for SF compared with CD. Even the most intensive sampling regimen did not allow an acceptable prediction of daily mean PDIc or Ale ratio, minimum r values for PDIc and Ale ratios were 0·098, 0·136 and 0·547, 0·579 for SF and CD, respectively. Furthermore, daily mean PDIc and Ale ratios proved poor predictors of daily PD and allantoin excretion (r values of 0·69 and 0·72, respectively). Total urine collection appears necessary to assess accurately daily PD excretion in dairy cows.

Sixteen varied grass silages metabolizable energy (ME): 9·76 to 11·99 MJ/kg ethanol-corrected toluene dry matter (TDM); crude protein (CP: 149 to 211 g/kg TDM; lactic acid: 3·5 to 134·7 g/kg TDM; butyric acid 0·4 to 46·7 g/kg TDM) were offered ad libitum to early-lactation dairy cows (12 per experiment) along with a fixed allocation of 7 kg/day of a standard concentrate. Four silages were offered in each of four incomplete change-over design experiments with three 21-day periods. This design meant that each cow was allocated to receive three of the four silages evaluated in that experiment. ME intake ranged from 108 to 262 MJ/day (mean 177 (s.d. 30·2)). Similar variation was obtained with milk yields (mean 26·5 (s.d. 4·36) kg/day), fat content (mean 37·7 (s.d. 5·60) g/kg) and protein content (mean 29·0 (s.d. 2·36) g/kg). Urinary purine derivative/creatinine ratio (PD/C), an index of microbial protein measured in spot samples (two per day) averaged 2·92 (s.d. 0·757) mol/mol. Allantoin made up an almost constant molar proportion of PD excretion (mean 0·876 (s.d. 0·0377)), with a small but significant (P < 0·001) decline of 0·0132 (s.d. 0·003) per unit increase in PD/C.Maximal utilization of silage nitrogen occurred with silages having higher ME and lower CP concentrations. Urinary PD/C suggested that microbial protein yield varied in a way which would not be predicted in current schemes and that it was a major source of variation in milk protein yield under the conditions of the present experiment. Principal components regression confirmed independent effects of ME supply and MP supply (indexed by urinary PD/C) on milk protein yield. Further work should pursue the possibility of using the urinary PD/C technique to refine protein feeding at the farm level.

Eight mid-lactation Holstein-Friesian dairy cows were used in an experiment to investigate whether poor transfer to milk of (n-3) long chain (≥C20) poly-unsaturated fatty acids (n-3 LCPUFA), from diets containing fish oil, is related to their mode of transport in plasma lipoproteins. The cows were split into two groups of four, each of which was housed with 24 other cows which did not provide blood data in this experiment. All cows received a basal diet ad libitum consisting of (kg/t dry matter) silage (539), grain distillers’ grains (148), rolled barley (248) and soya (65). All cows also received a mid-day meal of 2·76 kg per cow per day of molassed sugar-beet shreds. The control group (C) received no oil supplement but those in the treatment group (F) received 300 g per cow per day of fish oil absorbed onto the sugar-beet shreds. Fish oil inclusion progressively depressed milk fat concentration of the four cows from each group over the 3 weeks of the experiment so that levels were approximately 20 g/kg lower for cows in treatment F than for those in C (P < 0·05). Mean concentrations over all cows of the long-chain (≥C20, n-3) poly-unsaturated fatty acids in milk fat (g/100 g) were 0·12 and 0·54 for treatments C and F respectively, whilst corresponding output in milk (g/day) increased from 116 to 3·91, an average efficiency of transfer of 4·6%. The fatty acid compositions of the lipoproteins were measured in plasma samples from the four cows from each group after 3 weeks on the experimental diets The proportions (g/100 g fatty acids) of C20: 5 (n-3) in cholesteryl (CE) and phospholipid (PL) of high-density lipoprotein (HDL) in the plasma were respectively increased from 0·97 to 4·39 (P < 0·05) and from 1·15 to 4·74 (P < 0·01) by the fish-oil supplementation. For C22: 6 (n-3), the proportions in CE and PL of HDL respectively increased (P < 0·001) from 0·02 to 0·23 and from 0·16 to 2·18 as a result of the supplementation. The mean proportions (g/100 g fatty acids) of C20: 5 (n-3) and C22: 6 (n-3) in the triglyceride fraction of very low-density lipoprotein were 1·05 and 2·3 respectively and were not significantly altered by fish-oil supplementation (P > 0·05). It is suggested that the low transfer efficiency of (n-3) LCPUFA to the milk is partly due to their transport in the plasma largely as components of HDL lipids which are unavailable to the mammary gland.