Low protein diets based on high protein forages for dairy cows: effects on performance, metabolism and nitrogen use efficiency
Chowdhury, M.R. (2022) Low protein diets based on high protein forages for dairy cows: effects on performance, metabolism and nitrogen use efficiency. Doctoral thesis, Harper Adams University.
|
Text
Mohammed Chowdhury.pdf Download (5MB) | Preview |
Abstract
The effects of an increasing global price of soybean meal and tighter regulations on ammonia emissions, and the disposal of manure and slurry has led to renewed interest in alternative dietary protein strategies for dairy cows. The objectives of this thesis were to improve the nitrogen (N) use efficiency (NUE) of dairy cows whilst maintaining performance and reducing the environmental impact of milk production by feeding low crude protein (CP) diets based on high protein, home grown forage legumes. In Study 1, 18 early lactation Holstein-Friesian dairy cows were fed 1 of 3 diets based on 50:50 red clover to grass silage (dry matter (DM) basis) and 1 of 3 dietary CP levels: high (H) – 175 g CP/kg DM; medium (M) - 165 g CP/kg DM or low (L) – 150 g CP/kg DM. The diets were fed in a 3 x 3 Latin square design, with 3 periods of 28 days, with measurements undertaken in the final week of each period. The metabolisable protein (MP) supply was predicted to meet requirements in H and M, and be 95% of requirements in L. Cows fed L had an intake of 23.5 kg DM/d, some 1.5 kg DM/d lower than those fed H or M, but milk yield was similar across treatments, with a mean of 34.8 kg/d. The NUE was 20% higher in cows fed L than H. In Study 2, 18 multiparous Holstein-Friesian dairy cows were fed 1 of 3 dietary treatments: H50: high protein (172 g/kg DM) with 50:50 lucerne:maize silage (DM basis); L50: low protein (150 g/kg DM) with 50:50 lucerne:maize silage, and L60: low protein (150 g/kg DM) with 60:40 lucerne:maize silage. The diets were fed in a 3 x 3 Latin square design, with 3 periods of 28 days, with measurements undertaken in the final week of each period. All diets were formulated to meet MP requirements. Intake was higher in cows fed H50 vs. L50, with L60 being intermediate. Milk yield was also highest in cows fed H50 at 40.9 kg/d, and lowest in L60 at 38.9 kg/d, with L50 being intermediate. The NUE was 18% higher in cows fed L50 or L60 compared to H50. In Study 3, 56 Holstein-Friesian dairy cows were fed 1 of 4 diets based on 50:50 red clover to grass silage (DM basis). All diets were formulated to have a similar MP content and a CP concentration of 175 g/kg DM (high protein, C), 150 g/kg DM (low protein, LP), or LP supplemented with additional starch (LS) or rumen-protected methionine (LM). Reducing dietary CP from 175 to 150 g/kg DM did not affect DM intake, milk yield or composition, live weight or condition change. Reducing CP increased NUE by 20% and lowered urinary N excretion by 60 g N/d. In Study 4, a systematic review and meta-analysis was conducted to investigate the effects of dietary CP concentration on the performance, metabolism and NUE of dairy cows fed forage legume-based rations. A total of 36 studies with 102 treatment means were included. The mean CP content of the control and low CP diets was 171 and 145 g/kg DM respectively. On average, lowering dietary CP reduced DM intake by 0.6 kg/d, milk yield by 1.4 kg/d and milk protein content by 0.2 g/kg, but increased NUE by 4% units. In conclusion, low CP diets improve NUE without affecting milk performance if MP requirements are met.
| Item Type: | Thesis (Doctoral) |
|---|---|
| Divisions: | Agriculture and Environment (from 1.08.20) |
| Depositing User: | Ms Kath Osborn |
| Date Deposited: | 03 May 2022 10:57 |
| Last Modified: | 03 May 2022 10:57 |
| URI: | https://hau.repository.guildhe.ac.uk/id/eprint/17833 |
Actions (login required)
 |
Edit Item |