Energy evaluation of fresh grass in the diets of lactating dairy cows

Abstract

The discrepancy between the estimated feeding value of fresh grass and the output per kg grass in terms of milk and maintenance was studied by evaluating 12 experiments with grass-fed dairy cows. The percentage grass in the diets varied between 40 and 90. Intake and milk production were recorded daily.Per treatment a number of parameters relating to the composition of the grass, characteristics of the animals, and composition of the total diet were determined. The correlation between each of these parameters and the measured discrepancy was calculated. The digestible organic matter in the grass (DOM), intake of grass, intestinal digestible protein in the total diet, percentage milk protein and body weight gain correlated well with the discrepancy. It was concluded that energy input from grass and energy output in milk production were significantly different (P < 0.05). For the diets with 80-90% grass a high DOM increased discrepancy.It was furthermore concluded that the maintenance requirements of lactating dairy cows fed grass-based diets are probably higher than the currently used values This was ascribed to energy requirements in the gastro-intestinal tract and to nitrogen excretion.

N- en P-excretie melkvee: achtergronden en bronnen voor de berekening

“…Een deel wordt toegeschreven aan voerverliezen (2%) en onjuiste inschatting van de VEM-behoefte of opname. Een onjuiste inschatting (onderschatting) van de VEM-behoefte en/of opname kan worden toeschreven aan een slechtere vertering van voer door zieke dieren, suboptimale voeding, een onjuiste (te hoge) inschatting van de voederwaarde van ruwvoer (Bruinenberg et al, 2002a;Bruinenberg et al, 2002b) of onderschatting van de onderhoudsbehoefte van hoogproductief melkvee (Dong et al, 2015). Recente studies met energiebalans data van melkkoeien gemeten in respiratiecellen laten zien dat de onderhoudsbehoefte van melkkoeien de laatste decennia is toegenomen, maar daar staat tegenover dat de efficiëntie waarmee metaboliseerbare energie wordt gebruikt voor melkproductie ook is toegenomen (Moraes et al, 2015).…”

Effect of exchanging Onobrychis viciifolia and Lotus corniculatus for Medicago sativa on ruminal fermentation and nitrogen turnover in dairy cows

“…The absorption and metabolism of this NH 3 then elevates the urea levels in the blood, milk, and urine (Roseler et al, 1993;Spek et al, 2013). Bruinenberg et al (2002) reported a frequently high excretion of N in the urine due to the imbalance between dietary protein and energy content in herbage-fed cows. This excretion has adverse environmental effects (Dijkstra et al, 2013), and it may also increase the metabolic load, especially during early lactation, because of the extra energy consumption needed for detoxification of excessive ruminal ammonia by ureagenesis (Lobley et al, 1995).…”

“…This excretion has adverse environmental effects (Dijkstra et al, 2013), and it may also increase the metabolic load, especially during early lactation, because of the extra energy consumption needed for detoxification of excessive ruminal ammonia by ureagenesis (Lobley et al, 1995). Furthermore, the reduced flux of (microbial) protein to the duodenum, as a consequence of low dietary supply of fermentable energy, is supposed to be a limiting factor for milk production in cows consuming herbage (Bruinenberg et al, 2002). Therefore, forage-based diets have to be designed in a way that must prevent excessive ruminal protein degradation and increase the amount of ruminal escape protein, thereby increasing the digestive and metabolic N efficiency.…”

Prediction of metabolisable energy concentrations of fresh-cut grass using digestibility data measured with non-pregnant non-lactating cows

“…However, if EE is not available in practice, adding just WSC and ADF as predictors may not improve prediction accuracy, but, in the present study, it still reduced standard error and the difference between predicted and actual values by 13 and 32 % respectively, explaining the variation further when compared with the equation using DE as the sole predictor. The positive association between WSC, EE and ADF with ME can be explained by (1) the fact that these nutrients would be the main source of energy for N utilisation by rumen microbes and (2) the negative relation of grass N with WSC and fibre contents (27,29) ; these two features would decrease energy losses related to excess N metabolism and excretion (9) . The significant effect of grass N on the prediction of ME may be explained by the fact that the difference between DE and ME is highly dependent on energy excretion in urine, and consequently on N intakes and outputs (24) .…”