FAT SUPPLEMENTATION AS AFFECTED BY FORAGE FIBRE IN DIETS OF HIGH-PRODUCING COWS

Supplementation with fats or fatty acid complexes in diets of high producing cows has the goal of increasing overall energy intake to meet the requirements for the high level of milk synthesis and at the same time to limit the loss in body reserves, since a substantial loss has negative consequences for reproduction and the inter-calving period. A second principle is that if the high energy requirement is to be met by starch such as in maize, rumen function may be disturbed, resulting in sub-clinical acidosis, lowered intake etc. However, fat supplementation has limitations too, as high levels may reduce fibre digestibility and forage intake. Therefore, the ideal balance is sometimes difficult to find and the subject of many studies. The study discussed below is comprehensive and is particularly interesting, as one doesn’t often see investigations with cows yielding 50 litres milk per day. The study of Dr P. Piantoni and co-workers was published in two papers in the Journal of Dairy Science, Volume 98 of 2015, respectively on pages: 3309 to 3322 and 3323 to 3334, with the titles: Saturated fat supplementation interacts with dietary forage neutral detergent fiber content during the immediate postpartum and carryover periods in Holstein cows: Production responses and digestibility of nutrients and Saturated fat supplementation interacts with dietary forage neutral detergent fiber content during the immediate postpartum period in Holstein cows: Energy balance and metabolism.

The authors allocated 48 multi-lactation cows to an experiment with a 2 × 2 factorial arrangement of two forage fibre and two fat supplementation treatments, to study the interaction between a highly saturated free fatty acid supplement (SFFA) and dietary forage fibre, measured as neutral detergent fibre (fNDF). They investigated production responses and energy utilization in early lactation. The four diets were offered from day 1 to day 29 post-calving (referred to as the post-calving period) and contained either 20 or 26% fNDF (50:50 ratio of maize silage and lucerne silage and hay, on a dry matter basis) and either 0 or 2% SFFA of a commercial mixture. From day 30 to day 71 in lactation (referred to as the carryover period), a common diet (23% fNDF, 0% SFFA) was offered to all cows to evaluate carryover effects of the treatment diets provided during the post-calving period.

During the post-calving period, the higher (26%) fNDF decreased dry matter intake (DMI) by 2.0 kg per day, whereas the 2% SFFA supplementation increased it by 1.4 kg per day. In addition, the high fNDF with 0% SFFA decreased DMI compared with the other diets and this difference increased from day 1 to day 29. The treatments, however, did not affect the 3.5% fat-corrected milk yield, but did so during the carryover period when SFFA supplementation decreased 3.5% fat-corrected milk yield for the low (20%) fNDF diet (51.1 versus 58.7 kg per day), but not for the high-fNDF diet (58.5 versus 58.0 kg per day). During the post-calving period, the low fNDF and SFFA supplementation decreased body condition score loss. This was reflected in a tendency for an interaction between fNDF and SFFA which indicated that the low fNDF with 2% SFFA decreased body condition score loss more compared with the other diets (−0.49 versus −0.89 units). However, the low fNDF and 2% SFFA supplementation decreased feed efficiency (3.5% fat-corrected milk per kg DMI) by 0.30 and 0.23 units, respectively. The effect declined towards 29 days post-calving. Supplementation with SFFA in the post-calving period favoured energy partitioning to body reserves and limited DMI depression for the high fNDF diet, which might allow higher fNDF diets to be fed to cows in the post-calving period. Interestingly, SFFA supplemented in the low fNDF diet during the post-calving period affected production negatively in the carryover period. Thus, the results showed that dietary fNDF and SFFA interacted, affecting performance in the post-calving period, with carryover effects when cows were fed a common diet later.

From the second report the results showed that low fNDF versus high fNDF and 2% SFFA versus 0% SFFA increased digestible energy intake (DEI). The low fNDF diet with SFFA increased energy balance compared with the other treatments early during the treatment period, but treatment differences diminished over time. Overall though, the low fNDF versus the high fNDF diets and 2% SFFA versus 0% SFFA improved energy balance, but decreased the efficiency of utilization of DEI for milk. The low fNDF diets increased plasma insulin and glucose concentrations and decreased plasma non-esterified fatty acid (NEFA) and β-hydroxybutyrate concentrations, as well as liver triglyceride content. Compared with 0% SFFA, 2% SFFA decreased plasma NEFA concentration during the first week post-calving and tended to decrease plasma NEFA overall throughout the treatment period, but did not affect liver triglyceride content. During a glucose tolerance test, the 2% SFFA increased plasma insulin concentration more in the low fNDF diet than in the high fNDF diet. After glucose infusion, the 2% SFFA treatment increased insulin by 64% when included in the low fNDF diet, but only by 5.2% when included in the high fNDF diet.  In summary, supplementation of 2% SFFA and low fNDF diets increased DEI and improved energy balance, but decreased the efficiency of utilization of DEI for milk production. Fat supplementation affected energy partitioning, increasing energy balance and decreasing body condition score loss, especially in the lower fNDF diet. The decrease in body condition score loss observed was likely related to an increase in plasma insulin concentration. Feeding SFFA in a low fNDF diet during the first 29 days post-calving might have primed the cows to limit fat mobilization at the expense of milk production.

Bottom line: The interaction between fat supplementation and forage fibre level (and by implication dietary concentrate level), shows that nutritionists should be careful when including extra fat in the diet, because the success will depend on the amount of fibre (therefore also starch, because less concentrate will be in the diet at higher fibre levels) and the stage of lactation as carry over effects should be expected.