Dietary protein oscillation: Effects on feed intake, lactation performance, and milk nitrogen efficiency in lactating dairy cows

Abstract

Limited research with growing ruminants indicates that oscillating (OS) dietary crude protein (CP) concentration may improve nitrogen use efficiency (NUE). Our aim was to determine if a total mixed ration (TMR) based on OS CP (48-h phases of 13.4% and 16.5% CP, respectively) would increase NUE of lactating dairy cows compared with a static CP TMR (ST; 14.9% CP). The experiment was a randomized complete block design with 50 cows [150 ± 61 (mean ± SD) d in milk]. Cows were blocked by parity, days in milk, and milk protein yield. On average, diets were equal in composition over the total experiment. Cows were milked twice daily, and 8 milk samples were collected in each 4-d period. Each 48 h of low-CP (LP) and high-CP (HP) TMR offered to OS cows corresponded to milk collected at milkings 1 to 4 and 5 to 8, respectively. Dry matter intake (mean = 25.5 kg/d for both treatment groups); yields of milk (mean = 31.5 kg/d for both treatment groups), protein, fat, lactose, and fat-and proteincorrected milk (mean = 33.6 kg/d for both treatment groups); and milk concentration of protein, fat, and lactose did not differ between treatments. However, milk urea concentration was higher for OS compared with ST (12.2 vs. 11.3 mg/dL). Body weight, body condition score, NUE, and feed efficiency were unaffected by OS. Apparent total-tract digestibility of dry matter (695 vs. 677 g/kg), organic matter (714 vs. 697 g/kg), CP (624 vs. 594 g/kg), neutral detergent fiber (530 vs. 499 g/ kg), and starch (976 vs. 973 g/kg) were higher for OS than for ST cows. Cows in OS responded transiently, and regression analysis of differences within block over time revealed changes in yield of milk (−531 g/d), milk protein (−25.6 g/d), and milk lactose (−16.7 g/d) in LP. Opposite effects were observed for yield of milk (+612 g/d), milk protein (+28.8 g/d), and milk lactose (+28.0 g/d) during HP. Changes in concentrations of milk protein (−0.050%/d), lactose (+0.030%/d), and urea (−3.0 mg/dL per day) during LP, and in milk lactose (−0.024%/d) and urea (+4.3 mg/dL per day) during HP, were observed. Milk yield, lactose yield, and protein yield were lower for OS than ST cows at the last milking of LP and at the first milking of HP. Milk urea concentration did not show such a lag and was lower in the last 2 milkings of LP, and higher in the last 3 milkings of HP, in OS compared with ST cows. Overall, performance and NUE were unaffected by OS treatment, but apparent total-tract digestibility and milk urea concentration increased, and transient effects on milk yield and composition occurred in OS cows.

Protein nutrition of dairy cows : Some relevant further aspects of protein nutrition of dairy cattle, when reducing protein nutrition in dairy cows in view of societal demands

“…If oscillating dietary protein would result in a "down regulation" of renal urea excretion in urine or an increase in "renal urea recycling", as an adaptation mechanism to "conserve" nitrogen, this would likely result in increased concentrations of plasma urea-N (PUN), milk urea-N (MUN), and possibly also ruminal NH3 compared to "static" CP diets. With respect to the study of Tebbe and Weiss (2020) the MUN level of the OSC diet tended (P<0.10) to be higher (with 0.7 mg/dL) than the static 14.1% CP diet, and in Rauch et al (2021) a significantly greater MUN level (0.4 mg/dL greater) of the OSC diet was reported. However, in the study of Brown (2014) no significant effect of OSC was observed, and likewise no effect was observed in the study of Köhler (2016) although numerically the OSC-48 h diet had a 1.0 mg/dL higher MUN than the static CP diet.…”

“…This difference was not observed in PUN concentrations however (PUN in static diet and OSC-48 diets were 20.0 and 20.2 mg/dL, resp.). Furthermore, apparent total tract digestibility of CP (TTD-CP; %) of the OSC diets in the study of Rauch et al (2021), Tebbe and Weiss (2020) and the OSC-48 diet in the study of Köhler (2016) were higher than for the respective static diets, and this may underlie the differences in MUN.…”

“…Lactating cows have a much higher protein requirement and feeding level compared to sheep and beef cattle which poses different challenges to protein metabolism and includes the metabolically highly active mammary gland. More recently, the effect of feeding oscillating dietary protein to lactating dairy cattle has been studied and reported in a few MSc theses (Brown, 2014;Köhler, 2016) and in peer-reviewed papers of Tebbe and Weiss (2020) and Rauch et al (2021). In the next section the results of these studies will be discussed in more detail and results are listed in Table 2.1…”

“…Results and discussion on results dairy cattle Table 2.1 summarizes the results of the four protein oscillation studies with lactating dairy cattle (Brown, 2014;Köhler, 2016;Tebbe & Weiss, 2020;Rauch et al, 2021). These studies were carried out with high producing cows (32 -38 kg milk/d) demonstrating a high DM intake (22 -27 kg/d).…”

Use of fat-soluble vitamins and feed additives in cow diets

“…And when adding different doses of the phytocomplex to the diet, its structure consisted of silage -20.0%, haylage -32.8% and compound feed -31.3%. The provision of the body of cows and milk with basic nutrients and biologically active substances, in particular, vitamins, was achieved through the inclusion of hay, silage, haylage, compound feed and feed additives in the diets [9]. The diets of cows using different doses of "Vitaminol" and the phyto-complex (separately) contained the following nutrients (Table 2).…”