Effect of the levels of N fertilizer, grass and supplementary feeds on nitrogen composition and renneting properties of milk from cows at pasture

Abstract

In a 2 x 2 x 3 factorial design grazing experiment we investigated the effect of fertilizer (none or 240 kg N/ha), amounts of clover grass available (low or high) and type and level of daily supplementary feed for each cow (3 -5 kg barley, 35 kg concentrate mixture rich in protein and fat, or both, 7 kg) on the protein composition and renneting properties of their milk. The experiment was carried out in two successive grazing seasons (years) and included a total of 79 Danish Holstein cows. The effect on milk protein composition was determined in both years whereas the effect on renneting properties was determined only in the second year. Fertilization of the clover grass significantly decreased total milk protein concentration (-1-4 g/kg; P < O01) and tended also to decrease the relative proportion of whey protein N. Fertilization had no effect on renneting properties. Increased availability of clover grass significantly increased milk protein concentration (1 g/kg; P < 0-05) and resulted in significantly poorer renneting properties, that is increased clotting time (P<O01) and decreased coagulum development. These effects seemed to be mediated through an effect on the pH of the milk (+ 0 -05; P < 0 -05) as the effect was markedly reduced when statistical correction was made for the actual pH. Use of the protein-and fat-rich concentrate mix (3 -5 kg) significantly reduced the total protein content of the milk (P < 0-05) and increased the proportion of non-protein N (NPN) in total N compared with use of the other supplementary feeds (P < 0-05). We found no effect on renneting properties of the different supplementary feeds. Throughout the grazing season and independent of the main treatments, the NPN proportion of milk N increased at the expense of casein N. At the same time, renneting properties became poorer, especially with high clover grass availability.

Effect of pasture allowance and energy supplementation upon dairy cows milk yield.

“…Los menores valores de urea, especialmente en leche, encontrados en vacas que recibieron el mayor nivel de SE, tienen sustento considerando las investigaciones realizadas por Castillo y Gallardo (1995), quienes plantearon la existencia de una estrecha relación entre suplementación energética de animales en pastoreo y nitrógeno no proteico en leche (R 2 =0,63). En el mismo sentido, Hermansen et al (1994), también en situaciones de pastoreo, midieron menores niveles de urea en plasma reemplazando un concentrado rico en grasa por un concentrado a base de carbohidratos que aportaba energía en rumen. Corbellini (1995) planteó que niveles de urea en leche superiores a 30 mg·dl -1 junto con porcentajes de proteína láctea inferiores a 3,2% indican défi cit de energía y exceso de proteína en la dieta.…”

Chemical composition and somatic cells count of milk from Holstein x Braunvieh cows

“…As Hermansen et al (1994), the casein contents have a positive correlation with the protein content of milk, since casein represents approximately 80% of total proteins of milk; therefore, in this study, the genetic groups that showed the highest protein levels consequently showed the highest casein levels. Zanela et al (2006) reported that the percentages of casein and solids are affected mainly by nutrition; however, as there was no difference in the diet in the present survey, it could be inferred that there is a close relationship between increased blood levels and increased casein content in milk.…”

A model to secure a stable iodine concentration in milk

“…thiocyanate) ( 5 , 17 , 20 ). However, high or low GSL intake seems to be of minor importance, as the differences found in iodine and thiocyanate concentrations in milk between different levels of GSL intake were low ( 18 , 30 ). However, there are considerable differences in milk iodine levels when feeds with and without rapeseed products are offered ( 5 , 30 ).…”

“…However, high or low GSL intake seems to be of minor importance, as the differences found in iodine and thiocyanate concentrations in milk between different levels of GSL intake were low ( 18 , 30 ). However, there are considerable differences in milk iodine levels when feeds with and without rapeseed products are offered ( 5 , 30 ). In contrast to previous models ( 5 , 24 – 26 ), the models in the present study included intake of GSL or rapeseed products in addition to iodine as variables in the same model.…”