Abstract
The study utilised a pasture grazing based, voluntary traffic automatic milking system to investigate milk production of cows fed a pasture-based diet and supplemented with a pellet formulated with vs. without rumen-protected lysine and methionine (RPLM). The study adopted a switch-over design (over two periods of 5 and 10 weeks, respectively) and used 36 cows and equally allocated them into two experimental groups. The RPLM (Trial) pellet had 2% lower crude protein, but similar metabolizable energy content compared to the Control pellet. Pellet intake was 10.0 and 9.4 kg/day/cow. Milk yield was 36.2 and 34.4 kg/day/cow (p = 0.23), and energy corrected milk was 35.1 and 33.8 kg/day/cow (p = 0.076), and milk solids was 2.55 and 2.46 kg/cow/day (p = 0.073) in the Control and Trial groups, respectively. Milk fat%, milk protein%, milk fat: protein ratio, milking frequency and rumination time were not different between the two groups (p > 0.05). In period 1, plasma glucose was 3.1 mmol/L for both groups and milk urea were 150 and 127 mg/L in the Control and Trial groups, respectively. Both plasma glucose (as a proxy for energy supply) and milk urea (as a proxy for nitrogen use efficiency; NUE) were not different between groups (p > 0.05). This study showed that under a grazing pasture system, feeding lactating dairy cows a low protein pellet with RPLM supplementation, maintained milk production performance and NUE, compared with cows fed a high protein Control pellet diet with no RPLM. Further research should assess the long-term (seasonal) effects of feeding a diet formulated with RPLM on cow intake, health and reproductive performance.
Highlights
Methionine (Met) and lysine (Lys) are often the first two limiting amino acids (AA)in the lactating dairy cow diet [1,2,3]
In an earlier study, lactating dairy cows fed on a soybean meal-based diet supplemented with Met had a higher milk yield and milk protein yield than those ones fed with only soybean meal [6]
The formulated pellet with rumen-protected lysine and methionine (RPLM) had approximately 2% lower crude protein (CP), but similar metabolizable energy (ME) content compared to the Control pellet (Table 2)
Summary
In the lactating dairy cow diet [1,2,3]. The effects of supplementing dairy cows with Met and Lys were previously investigated in total mixed ration (TMR) systems, in European countries and United States [4,5]. In an earlier study, lactating dairy cows fed on a soybean meal-based diet supplemented with Met had a higher milk yield and milk protein yield than those ones fed with only soybean meal [6]. Lys and Met supplementation in lactating dairy cow diets stimulated feed intake, milk yield and milk protein%. There was limited or no improvement in feed intake and milk production performance in dairy cows supplemented with Met and Lys. For example, Rogers et al [1] showed that
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