Validation of metabolisable protein and energy systems to predict the productivity of meat goats fed tropical grass, legumes and protein supplements

Aoetpah, Aholiab (2019) Validation of metabolisable protein and energy systems to predict the productivity of meat goats fed tropical grass, legumes and protein supplements. PhD thesis, James Cook University.

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Tropical pastures are dominated by tropical or C4 grasses, which supply most of the forage material for grazing meat goats. In the typically long dry season of Northern Australia and West Timor, Indonesia, these grasses contain crude protein (CP) of 20 to 100 g/kg DM. This is equivalent to metabolisable protein (MP) content of 10.5 to 60.9 g/kg DM and metabolisable energy (ME) of 6.2 to 9.1 MJ/kgDM. These cannot meet the goats' requirements for MP and ME as recommended by the National Research Council (NRC) 2007. These nutritional issues cause low productivity in periparturient does for breeding and in weaner kids raised for red meat production.

A feeding strategy aimed at increasing the productivity of goats fed tropical grass hay was to provide protein supplements to meet the ammonia requirements for rumen microbes with the minimum requirement 20 to 50 mg N/litre (Nolan, 1981) and true protein for the animals.

Four general objectives were defined for this thesis:

• To meet the nutrient requirements of periparturient and lactating does and weaner kids for both rumen degradable and undegradable protein (RDP and UDP), from which metabolisable protein (MP) was derived.

• To categorise diets based on the relative and total estimated amounts of RDP, UDP, MP as well as metabolisable energy (ME) based on organic matter digestibility.

• To validate the NRC (2007) methodologies for the prediction of dry matter intake (DMI) and average daily gain (ADG) of weaner kids fed tropical forages using intakes of these protein fractions and ME.

• To recommend supplementation strategies that incorporate the RDP and UDP supplied by diets to improve growth and carcass yields of meat goats in the tropics, especially in East Nusa Tenggara (West Timor), Indonesia.

Four experiments were conducted and each experiment became one chapter of this thesis. Experiment 1 utilised twelve periparturient crossbred Boer does and their suckling kids. Each group of three animlas was offered Rhodes grass hay (RGH) as a basal diet (Control) or RGH supplemented with urea (Urea), urea plus cottonseed meal (Urea-CSM) and cottonseed meal (CSM). The objectives were to limit doe body weight loss, prevent ketosis and to increase the ADG of their suckling kids by varying the quantities of UDP and RDP based on the NRC (2007) recommendation. Protein supplements did not prevent doe body weight loss, but Urea-CSM and CSM supplements reduced non-esterified fatty acids (NEFA) and β-hydroxybutyrate (BHB) in the blood plasma. Supplements did not affect milk concentration, but increased ADG in suckling kids in the first week of the lactation period. These body weights and blood metabolites responses were associated with intakes of UDP, RDP, ME and Nitrogen retention.

Experiments 2 and 3 were conducted to increase liveweight gain and carcass yield of crossbred Boer goats by varying the quantities of dietary concentrations of RDP and UDP according to NRC (2007) recommendation. In a five-treatment experimental design, the basal diet of Rhodes grass hay was supplemented with:

1. Urea (Urea),

2. Urea plus cottonseed meal (Urea-CSM),

3. Cottonseed meal (CSM),

4. Air dried Gliricidia sepium leaves (Gliricidia), and

5. Desmanthus leptophyllus dried leaves (Desmanthus) only.

The dietary crude protein concentrations in Experiments 2 and 3 were 137 g/kg DM and 195 g/kg DM, respectively. Five of the 25 growing female crossbred Boer kids were allotted one diet in Experiment 2 for 120 days. The results showed that goats supplemented with Urea, Urea-CSM or Gliricidia lost weight as much as 15, 3 or 3 g/head per day, respectively.. Goats supplemented with CSM gained weight at the rate of 7 g/d and this increased to 33 g/d when the goats were fed Desmanthus hay. This liveweight gain data was not associated with MP and ME requirements suggested for temperate goats by NRC (2007). Growing at these rates, it was apparent that weaner goats would not achieve market liveweight within a reasonable timeframe. Therefore, Experiment 3 was conducted by increasing the dietary crude protein concentration to 195 g CP/kg DM.

In Experiment 3, the goats were rearranged into the same five dietary treatments and raised indoors in individual pens for 130 days. Evidence from this study revealed that weaner goats fed Desmanthus grew faster at an ADG of 83 g/head per day and had heavier carcass with an average cold carcass weight of 12.1 kg and non-carcass components, followed by goats fed CSM, Urea-CSM, Gliricidia and Urea. Heavier carcass weight was associated with greater eye muscle area and fat depth at the 12th to 13th rib interface. The higher rate of liveweight gain, carcass and non-carcass components yields for goats fed the Desmanthus diet, compared with other treatments, was associated with increased intakes of UDP, RDP, MP and ME.

High intakes, growth rate and carcass weight in the goats was more likely associated with feed digestibility and nitrogen retention. Experiment 4 was therefore conducted to compare apparent digestibility and nitrogen retention in crossbred Boer kids fed tropical grass hay supplemented with an NPN-RDP source (urea) and a source of RDP and UDP of true protein origin (cottonseed meal) at a dietary crude protein level of 175 g/kg DM. Twelve growing, male crossbred goats were divided into four groups of three. The first, a control group, received a basal diet of RGH; the second, a Urea group, received RGH plus urea; the third, a Urea-CSM group, received RGH plus urea mixed with cottonseed meal and the fourth, a CSM group, received RGH plus cottonseed meal. Results indicated that higher feed intake, apparent digestibility of crude protein and digestible nutrient intake were associated with CSM and Urea-CSM supplements. Higher nitrogen retention, however, was associated with CSM supplementation.

Modeling to predict DMI and ADG was conducted using input data derived from Experiments 2 and 3. Dry matter intake was predicted using metabolic body weight and estimated dietary concentration of ME or DM digestibility or estimated dietary concentration of ME only. Results showed that these equations were generally not useful to predict DMI of goats. Specifically, it was evident that dietary concentration of UDP, not RDP or CP, was the better predictor of DMI. When ADG was predicted using MP and ME intakes incorporated with standard requirements by NRC (2007), the percentage of variation explained by the model as indicated by the coefficient of determination (R²) was so low that the difference between predicted and actual ADG values was very large, hence predictability was poor. Metabolisable protein intake could predict ADG when goats were supplemented with Urea or fed Desmanthus only at a dietary CP level of 137 g/kg DM. Metabolisable energy intake could only predict ADG in goats supplemented with Gliricidia at a dietary CP level of 195 g/kg DM. Despite the high coefficient of determination (R²) values above 0.70, a strong relationship between ADG and MP or ME intake in these two studies was not evident since the NRC (2007) equations could not accurately predict ADG for most of the treatments.

It can be concluded that protein supplementation to goats fed tropical grass should consider requirement for rumen microbes in the form RDP and the requirement for animal in the form of UDP. The combination of these two types of protein sources made of Urea and cottonseed meal at the dietary crude protein level of 143 g/kg DM maintained normal blood metabolites of periparturient does. Supplements of Urea, Urea plus cottonseed meal or cottonseed meal to lactating does increased average daily gain of suckling kids but weaner goats should be supplemented with RDP and UDP at a dietary crude protein level of 195 g/kg DM. Dry matter intake and ADG responses were associated with intakes of RDP, UDP and ME. Among these determinant factors, UDP is the best predictor for DMI. Both intakes of MP and ME were good predictors for ADG of weaner kids according to the NRC (2007) prediction methodologies. In addition to Urea and cottonseed meal, Desmanthus hay provides RDP and UDP for weaner goats, which resulted in heavier body weight and carcass weight as compared to those fed Rhodes grass hay and supplemented with Urea and/or cottonseed meal.

Item ID: 60615
Item Type: Thesis (PhD)
Keywords: carcass, degradable/undegradable protein, energy, goat meat, goats, metabolisable energy, metabolisable protein, periparturient does, prediction, production, protein, supplementation, tropical pasture
Copyright Information: Copyright © 2019 Aholiab Aoetpah.
Date Deposited: 14 Oct 2019 23:40
FoR Codes: 07 AGRICULTURAL AND VETERINARY SCIENCES > 0703 Crop and Pasture Production > 070302 Agronomy @ 50%
07 AGRICULTURAL AND VETERINARY SCIENCES > 0702 Animal Production > 070202 Animal Growth and Development @ 50%
SEO Codes: 83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8304 Pasture, Browse and Fodder Crops > 830406 Sown Pastures (excl. Lucerne) @ 70%
83 ANIMAL PRODUCTION AND ANIMAL PRIMARY PRODUCTS > 8303 Livestock Raising > 830304 Goats @ 30%
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