Dairy goats adjust their meal patterns to the fibre content of the diet

Few studies have investigated how meal patterns of ruminants are affected by diet fibre content. Dairy goats (N = 32) in late lactation and early gestation were housed in eight groups of four goats, with all combinations of breed (Alpine and Saanen) and lactation number (1 and 2) represented in each group. Each goat had access to its own individual feed trough placed on a weigh scale with data logged automatically. All goats were fed the same total mixed ration (TMR; 30% concentrate and 44.6% NDF in DM) ad libitum for a control period of 22 days. Using the same feed ingredients, half of the groups were then offered a High fibre diet (20% concentrate; 47.3% NDF), and the other half a Low fibre diet (40% concentrate; 41.5% NDF) for a treatment period of 16 days. Daily meal patterns (meal frequency, duration and size, feeding rate, daily feed intake and daily feeding time) were computed for each animal using a meal criterion of 8 min. The last 10 days for each period (control and treatment) were used to calculate individual period means and individual differences between the two periods. During the control period, the goats ate on average 12.1 ± 0.49 meals/day, consuming 4.2 ± 0.10 kg fresh TMR daily. When the ration changed, all measures of feeding behaviour except meal size changed asymmetrically for the goats on the two diets. Goats fed the High fibre diet reduced their meal frequency by 10%, and the first meal after feed distribution lasted 11% longer, leading to a 9% reduction in feeding rate and no significant changes in daily feed intake and daily feeding time. Goats on the Low fibre diet did not significantly change their meal frequency or meal size, but the combined changes nevertheless led to a 9% increase in daily feed intake. On the Low fibre diet, goats were able to increase their feeding rate by a third, leading to a reduction in meal durations, thus reducing daily feeding time by 13%. Goats adapt their feeding behaviour to the fibre proportion of the offered diet, with more changes when fibre content is lowered, which needs to be taken into account when comparing phenotypes and adaptability of small ruminants to different diets.

Relationships of both urine nitrogen output and plasma urea concentration with rumen protein balance in lactating goats

The updated INRA system incorporates the notion of rumen protein balance (RPB, g CP/kg DM) in an attempt to better fit feed evaluation, animal requirements and responses to diets. RPB is the difference between crude protein intake and entrance at the duodenum (excluding NH3) which is not very easy to measure in vivo. The aim of this study was to test the strength of the relationships between dietary RPB values obtained from the diet composition and criteria easier to measure, such as N urinary outputs or plasma urea concentration, both at a treatment level and at an individual level in a large dataset obtained from lactating goats fed different types of diets. RPB was a better predictor of urinary N output and plasma urea concentration than was the former French system for protein digestible in the intestine. Within experiments, RPB was highly and positively correlated with urinary nitrogen outputs and plasma urea concentration. RPB can be used to estimate the urinary N output in lactating dairy goats, but this study also showed that some of the residual variance was due to variability among animals.

Relationship between CH4 and urinary N outputs in ruminants fed forages: a meta-analysis of the literature

Enteric methane (CH4) and faecal and urinary nitrogen (N) are two major pollutants due to ruminants. However, relations between these two components have been seldom studied, and the specific relationships for forage diets are not known. A meta-analysis was conducted using a large database of published data for ruminants fed forages, in which CH4 production, digestibility and urinary N (UN) output were all available. A total of 148 treatments (55 from cattle and 93 from small ruminants) from 29 publications and 56 experiments were used. Globally, there was a positive relationship between CH4 and UN production when expressed either per kg of liveweight or per kg of dry matter (DMI) intake. These relationships were maintained when a subset of 38 experiments that focussed on the influence of variation of DMI were considered. Otherwise, when a subset of 17 experiments that focussed on forage crude protein content were considered, the two equations relating CH4 and UN remained significant but the slopes were much smaller. In conclusion, the positive relationship between CH4 and UN can be mainly explained by the indirect positive influences of DMI or of diet organic matter digestibility on these two parameters.

Effects of the percentage of concentrate on rumen fermentation, nutrient digestibility, plasma metabolites, and milk composition in mid-lactation goats

The aim of this work was to study the effects of the dietary percentage of concentrate on patterns of intake, the evolution of rumen fermentation characteristics and plasma metabolites after a meal, nutrient digestibility, and milk production and composition in a medium-term trial in dairy goats. These effects have been well studied in dairy cattle but seldom in goats. Thirteen ruminally and duodenally cannulated dairy goats (95±4 d in milk) fed ad libitum were used in this study. Goats were assigned to 1 of 2 dietary treatments: high-concentrate (70% concentrate on dry matter basis) or a low-concentrate (35%) total mixed rations. The experiment was conducted over a period of 10 wk, including 3 wk of adaption to the diets. Patterns of intake, rumen fermentation characteristics, and plasma metabolites after a meal and fatty acids profile of milk fat were compared at the onset and at the end of the experiment. The increase in dietary percentage of concentrate decreased rumen pH, acetate to propionate ratio, ammonia-N concentration, and plasma urea concentration. The percentage of concentrate did not affect total volatile fatty acid concentrations. The high-concentrate diet increased the rate of intake during the morning meal at the onset of the experiment, whereas it decreased total dry matter intake and the rate of intake during the morning meal at the end of the experiment. The high-concentrate diet resulted in greater organic matter digestibility. Raw milk yield and protein yield were greater in goats fed the high-concentrate diet, whereas fat yield was not affected by dietary treatments. The milk fat content was lower in goats fed the high-concentrate diet. Proportions of the trans-C18:1 isomer relative to total fatty acids in milk were higher with the high-concentrate diet, but no modification of the proportion of total trans-C18:1 was detected, in particular no shift from trans-11 C18:1 to trans-10 C18:1 was observed. Further, the isomer trans-10,cis-12 C18:2 was not detected. Data from this study could be used for a new modeling approach or to improve existing models.