Non-protein nitrogen (NPN) supplement: which fertilizer is commonly used in controlled amounts as a cattle-feed additive for ruminants?

Introduction / Context:
Ruminants (cattle, sheep) can utilize non-protein nitrogen sources because microbes in the rumen synthesize amino acids and microbial protein from ammonia and carbon skeletons. Urea, a high-analysis nitrogen compound, is therefore used in small, controlled quantities as a feed additive to boost the nitrogen supply to rumen microbes. The practice is highly regulated and must be managed carefully to avoid toxicity.

Given Data / Assumptions:

• The question asks which fertilizer doubles as an NPN feed.
• Rumen microbiota can convert urea → ammonia → microbial protein when sufficient fermentable energy is present.
• Dose control and mixing uniformity are essential for animal safety.

Concept / Approach:
Among the listed fertilizers, only urea is widely recognized and intentionally used as an NPN supplement for ruminants. CAN, SSP, and ammonium sulfate are plant nutrients and not fed as NPN sources; they also contain components (e.g., nitrate, sulfate) that are inappropriate or risky for feed usage in that manner.

Step-by-Step Solution:
Identify ruminant NPN source: feed-grade urea.Understand conversion: urea → NH3 in rumen; microbes incorporate N into amino acids.Check alternatives: CAN, SSP, ammonium sulfate are not used as feed NPN additives.Select urea.

Verification / Alternative check:
Animal nutrition guides specify allowable inclusion rates for feed-grade urea and warn about mixing thoroughly with carbohydrate feeds to prevent ammonia surges.

Why Other Options Are Wrong:
CAN: nitrate content poses methemoglobinemia risk; not a standard feed additive.SSP: a phosphate fertilizer; not an NPN source.Ammonium sulfate: not safely used as an NPN feed; sulfate can create imbalances.

Common Pitfalls:
Applying urea intended for fertilizer rather than feed-grade urea; overdosing without adequate readily fermentable carbohydrates; offering to non-ruminants, which cannot utilize NPN.

Final Answer:
Urea