The ingredient and chemical composition of the DPKC diets are provided in Table 1. Although the diets are iso-nitrogenous, the NDF and ADF fractions were markedly higher in DPKC 45 diets. Similar pattern of higher fiber fractions with DPKC inclusion was reported by van
Wyngaard and Meeske (2017). The higher fibre per cent of DPKC-included diets is attributed to the significant proportion of fibre-rich pericarp (35%) within the expeller cake
(Pickard, 2005).
The nutrient intake and digestibility coefficients are presented in Table 2. Despite the higher fibre content and lower palatability compared to cotton seed cake, the DPKC diets did not affect intakes of DM, DCP and TDN on gm per Kg0.75 body weight basis. Contrary to these results, few authors reported decreased nutrient intakes on feeding PKC diets
(Silva et al., 2013). In the current study, the negative effects of PKC on intakes might be masked by limited feeding (maintenance ration) as per the standard requirements, instead of feeding ad libitum. Moreover, mixing DPKC with other palatable feed ingredients such as rice, de-oiled rice bran and cotton seed meal might have ameliorated the anti-palatability nature of DPKC.
Including DPKC in the maintenance rations decreased the nutrient digestibility coefficients of dry matter, organic matter, crude protein, ether extract, crude fibre, nitrogen free extract, neutral detergent fibre, acid detergent fibre, hemi-cellulose and cellulose. The reduced digestibility coefficients could be attributed to the increased fibre content of diets included with DPKC, especially at higher levels (45%).
The rapidly fermentable N fraction of PKC is low with less effective degradability of protein compared to traditional protein sources, consequently reducing CP digestibility coefficient. Besides, the heat applied during oil extraction may cause Maillard reaction, rendering some portion of protein unavailable for rumen microbes. Similar results were reported on including PKC as high as 55%
(Silva et al., 2013) or 75%
(Chanjula et al., 2011) or 210 g/kg DMI
(Cruz et al., 2018) of the ruminants’ ration. On contrary,
Carvalho et al., (2006) observed no effect on nutrient digestibility coefficients of hay substituted with PKC at 15%, 30% and 45% level. Interestingly,
Cunha et al., (2013) revealed higher EE and NDF digestibility coefficients on feeding lactating dairy cows with PKC at 113, 228 and 342 g/kg DM. These inconsistencies could be connected to the roughage source. Supplementing unconventional protein sources to poor quality roughages may ameliorate the negative effects of the supplements, thereby masking the adverse effects
(Reddy et al., 2021). However, the buffalo bulls in the current study were fed high quality Super Napier fodder source.
Mineral balance of the buffalo bulls fed DPKC diets is presented in Table 3. The diets did not affect calcium and phosphorus balance. The calcium and phosphorus outgo in healthy ruminants depends on their intake levels; hence, the unaffected calcium and phosphorus balance could be related to their similar estimates in all the four replacement diets
(Reddy et al., 2019a and b). The experimental buffalo bulls were in positive nitrogen balance indicating that the DPKC diets met the digestible protein requirements. Nevertheless, the nitrogen outgo was higher and the N retention and per cent absorbed was lower for DPKC included diets. The higher nitrogen wastage is presumably instigated by low degradative ability of DPKC included diets.
The TVFA concentration and rumen nitrogen dynamics (total N, food and protozoal N and residual N) are presented in Table 4 and Fig 1. The TVFA concentration showed a linearly decreased pattern with increased DPKC inclusion levels (Fig 1a). Similarly,
Chanuja et al., (2010) reported a decreased TVFA concentration with increased DPKC inclusion from 15% to 55% of the diet. The decreased TVFA proportion could be connected to the decreased digestibility coefficients of organic matter and nitrogen free extract. Further, the ruminal nitrogen dynamics revealed decreased total nitrogen levels (Fig 1b) without affecting food and protozoal N (Fig 1c) and residual N (Fig 1d). The reduced rumen nitrogen content could be attributed to the decreased CP digestibility. A significant diet × time interaction was observed for all the rumen function parameters estimated. Overall, the post-hoc analysis revealed 30% as the optimum inclusion levels as the inclusion levels at 45% decreased dry matter digestibility, nitrogen retention and rumen nitrogen (Fig 2).
