Abstract:
Broiler production has become one of the most highly productive segments in the food production sector owed to the rapid change in consumer demand for affordable protein sources. The use of organic trace minerals has taken preference over the use of conventional inorganic sources, not only due to a higher efficacy and retention in the animal body, but also because of lower quantities needed in comparison to inorganic counterparts. However, due to the relative expense of organic trace minerals, higher inclusions of inorganic products are considered to be more cost-effective. The objective ofthis study was to investigate growth performance, carcass and breast meat quality characteristics of broilers fed inorganic or organic sources of zinc (Zn; ZnSO4 or Availa®Zn) and selenium (Se; sodium selenite (SS) or Availa®Se) relative to the duration of supplementation (0–32 days of age or 21–32 days of age) to construct a 4 x 2 factorial design. A three-phase feeding programme was implemented during the course of the trial; starter (0–10 d), grower (10–21 d) and finisher (21–32 d). A total of 1 920 one-day-old male Ross 308 broilers were randomly allocated to 1 of 8 dietary treatments (T). The control diet (T1) was formulated using 100 mg/kg Zn as ZnSO4 and 0.30 mg/kg Se as inorganic SS. The level of mineral supplementation was constant throughout the experimental treatments. Organic minerals were supplemented on an iso basis in T2, T3, and T4. Treatments 6, 7 and 8 contained 100% inorganic sources during the starter (0–10 d) and grower (10–21 d) period, whereby organic sources partially replaced inorganic sources during the finisher period (21–32 d). The treatments were as follows: T1 (100% ZnSO4, 100% SS; 0– 32 d); T2 (40% Availa®Zn, 100% SS; 0–32 d); T3 (100% ZnSO4, 50% Availa®Se; 0–32 d); T4 (40% Availa®Zn, 50% Availa®Se; 0–32 d); T5 (100% ZnSO4, 100% SS; 21–32 d); T6 (40% Availa®Zn, 100% SS; 21–32 d); T7 (100% ZnSO4, 50% Availa®Se; 21–32 d); T8 (40% Availa®Zn, 50% Availa®Se; 21–32 d), with 12 replicates each. Growth performance was evaluated at 7, 10, 14, 21, 28 and 32 days of age. Carcass and meat quality characteristics were evaluated after slaughter on day 32 and 34. Assessing the growth performance; body weight (BW), body weight gain (BWG), feed intake (FI), and feed conversion ratio (FCR) over the total feeding period, none of the treatments performed different from the control (P>0.05). Mineral source and duration of supplementation influenced 7-day body weight (P<0.10). The broilers utilised their feed more efficiently (P<0.05) when fed inorganic minerals in the starter phase (T1 and T6). However, broilers obtained better (P<0.05) feed efficiency results when inorganic sources were partially replaced with organic sources during the finisher phase (T5 and T7). Similarly, the partial supplementation of organic Zn and Se improved (P<0.05) FCR during the last week of the study compared to birds receiving organic Zn and Se from the start of the trial. Mineral source was shown to have an effect on FCR during the starter and grower phases (P<0.05). No treatment differences were observed on carcass characteristics
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measured in the study (P>0.05), although mineral source showed to yield heavier carcasses (P<0.10) when partially supplemented in organic form. The duration of supplementation showed to improv hot-carcass weight (P<0.05) when organic minerals were supplemented during the finisher phase on an iso basis. Breast meat pH, colour, drip and cook loss were comparable to the control group post-slaughter. Organic Zn supplementation from the start (T2) of the trial lowered the ultimate meat pH (P<0.10), whereby the combination of organic Zn and Se increased the ultimate meat pH (P<0.05). The duration of supplementation showed to be promising when organic minerals partially substituted inorganic sources in the finisher phase, indicating the potential to produce chicken meat on a least-cost basis while improving feed efficiency in later stages. Overall, birds fed diets partially supplemented with more bio- available sources of organic Zn and Se showed better results.
