Effects of forage-based diet on milk production and body reserves of dairy cows on smallholder farms in South Africa
Year: 2019
Type: dissertation
Abstract: Low nutrient intake affects metabolism and growth in pregnant heifers and limits milk production in lactating cows on communal area smallholder dairy farms of the subtropics.Two studies were conducted during the current research.The first study evaluated effects of nutrient supply in standardized dairy diets on the growth and body reserves of pregnant Jersey heifers raised on communal area smallholder farms in a semi-arid zone of South Africa.Twenty-two farms with a total of 42 heifers, aged 22 to 28 months which were seven months pregnant at the beginning of the study were selected for the study.These represented the total number of farms with dairy cows in the area that were supported through a structured Dairy Development Program (DDP) of South Africa.Each farm had at least two pregnant Jersey heifers during the summer season of 2016.Each heifer was supplied 2.5 kg of a far-off (60-30 d prepartum) dry cow concentrate and increased to 3.3 kg of the same concentrate at close-up period (29-0 d prepartum).Feeding of concentrate was based on a standardized feeding program as recommended by DDP.During this study, no feeding treatment was imposed on the heifers.Eragrostis curvula hay was supplied by DDP.Daily intake of 7.2 and 5.4 kg; respectively for heifers at 60-30 d prepartum and 29-0 d prepartum was determined based on residual hay.Heifer diet (HD1) and heifer diet HD2 were therefore simulated respectively for cows at 60-30 d preparpartum and 29-0 d prepartum, respectively.Diets were assessed for nutrient composition using chemical analyses and in vitro ruminal degradation.Post ruminal nutrient absorption and animal responses were predicted using the Large Ruminant Nutrition System (LRNS) version 1.0.33 (level 1).Actual measurements of body weight (BW), body condition score (BCS) were done and blood was collected and analysed for proteins monthly.Heifers' responses were validated against the model predicted values and comparative analysis of animal performance during pregnancy was done against the National Research Council (NRC, 2001) reference values.Relative to the minimum requirement for ruminants, both HD1 and HD2 diets had relative feed value (RFV) below 144.About 35% of HD1 dietary crude protein (CP) was within the slowly degrade neutral detergent fibre (NDF) fraction which is the neutral detergent fibre insoluble crude protein (NDFICP) while 32% was not available as the acid detergent insoluble crude protein (ADICP).Equally, HD2 diet had effectively 5.2% of CP as available protein and the fraction of the slowly degraded NDF constituted only 52.3% of the effective available protein.Energy density of HD1 and HD2 were 25% and 16% higher than expected at far-off and close-up period, respectively.The intake of metabolzable protein (MP) were 32 and 25% higher than predicted for the far-off and close-up period, respectively.Supply of MP was 37 % and was higher than NRC predictions of daily requirement in Jersey cow.This allowed BW gain of 29 kg and BCS of 0.33 which was within 25 th percentile for pregnant heifers.Mean concentration of blood urea at both far-off and close-up periods deviated by 25% from NRC values.Creatinine (CR) concentration was 145 μmol /L at far-off and 155 μmol /L at close-up period.The second study assessed the adequacy of two lactation diets fed to 42 primiparous Jersey cows, aged 24 to 30 months during early (1-30 d postpartum) and peak (31-60 d postpartum) periods on the lactation performance of the cows.Cows received 4.5 and 5 kg of dairy concentrate at 1-30 d postpartum and peak milk (31-60 d postpartum) respectively.Eragrostis curvula hay was supplied ad libitum and dry matter intake (DMI) was estimated at 7.2 kg of hay/cow/day from residual hay.No feeding treatment was imposed except for the standardised diets typical to the production environment.Two simulated lactation diets (LD1 and LD2) were prepared based on dry matter intake (DMI) of grass hay and lactation concentrate.Diets were assessed for v nutrient composition using wet chemistry and in vitro ruminal degradation.Nutrient supply of diets and absorption from the small intestines as well as cows' responses were predicted using the Large Ruminant Nutrition System (LRNS) version 1.0.33 (level 1).Body weight and BCS were monitored, blood was collected and analysed for proteins monthly.A record of milk yield was taken daily, and milk was analysed for fat, protein, lactose and urea nitrogen weekly.Cows had DMI of 11.2 kg which was 12% higher than the expected at 1-30 d postpartum period and 11.6 kg which was 21% higher than the expected in 31-60 d postpartum cows.Diets had low available protein as % of dietary protein (LD1=46%; LD2=45%) and the slowly degraded NDF fraction (NDFICP) constituted 64% of the available protein.Intake of energy was 20% and 17% lower than the predicted value for the cows, respectively, at 1-30 d postpartum and 31-60 d postpartum period.Cows had negative energy balance of -6.5 and -5.6 Mcal respectively at 1-30 d postpartum and 31-60 d postpartum cows.Protein intake of lactating cows was low, which resulted in negative protein balance of 59% and 42% of cow's daily requirement, respectively, at 1-30 d postpartum period and 31-60 d postpartum period.There was loss of BW and BCS, low milk yield, energy corrected milk (ECM: 9.50 kg/d) and feed efficiency (FE) of less than 1 (LD1= 0.85; LD2 =0.89) in cows at both periods.Composition of fat, protein and lactose in milk were negatively affected by the low level of dietary protein.Somatic cell count (SCC) in milk was 121 ± 13 x 10 3 /ml and cows did not show signs of illness.Mean milk urea nitrogen (MUN) concentration was 12 ± 2.7 mg/dl reflecting the low protein status of the lactating cows.Cows had high creatinine concentration of 116 and 102 μmol /L at 1-30 d postpartum and 31-61 d postpartum period, respectively, which may indicate muscle breakdown due to heat stress relative to the hot production environment.Results showed that diets fed to dairy cows on communal area smallholder farms in Sekhukhune and Vhembe districts in Limpopo province had low feeding value and their low nutrient supply affected rumen fermentation, heifers' 'growth, body reserves and early lactation in Jersey dairy cows.In conclusion, diets supplied to dairy cows raised on smallholder farms are low in nutrients and do not support efficient growth in heifers and optimal milk production in early lactation.Development of a nutrition plan for improved dairy diets is required to maximise production and longevity in cows and enhance sustainability of dairy production on the smallholder farms in South Africa.
Author: Modupeoluwa Comfort Akinsola
Language: English
Subfield: Animal Science and Zoology
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W2992848381